Four Layer Chocolate Mousse Cake

Four Layer Chocolate Mousse Cake

<alt img="Four Layer Chocolate Mousse Cake"/>

When each of my three sons’ birthdays rolls around, I ask what type of birthday cake they’d like even though I know what the answer will be without fail.

Chocolate.  Chocolate cake with chocolate frosting.  Chocolate with more chocolate on chocolate with chocolatey chocolateness, please.  You get the idea.

They know their mother writes this blog and loves to have a reason to post a new and different dessert — how perfect an excuse a birthday is!  But chocolate cake is all I’m asked for.  You’d think after more than six years writing here, I’d have posted nearly 20 different chocolate cakes, but I haven’t.  And I could have because true to form, I never make the same chocolate cake twice, but I’ve resisted, thinking what’s so special about a chocolate cake?  Is there anyone left on the planet who wants to read about a simple chocolate layer cake?  Truly, there must be millions of recipes available on the web at this point, with many professing to be the “very best,” “perfect,” or “homemade.”  No, I’m more of a renegade, tending to make chocolate desserts that are just outside the norm and do find that often they are not simple, but I think the very best, often nearly perfect (at least in flavor!), and always, always homemade.

Therefore, I fudge when I get the chocolate birthday cake request to sneak in a whipped cream filling with strawberries, or try a recipe with peanut butter mixed in.  There was a true low point in the cavalcade of chocolate birthday cakes when one of my sons mentioned the chocolate mint cake I’d made that year reminded him of toothpaste.  Nice.  That’s what I get for not making a simple chocolate birthday cake.  Perhaps it was the one year he requested mint chocolate and I complied.  Punishment for giving in to something that wasn’t exactly the chocolate cake I wanted to make.

So this year for my youngest son’s 21st birthday (yes, I am that young!) when the chocolate cake request came in, I decided to not stray from chocolate, but considered making a cake with a chocolate mousse filling.  In fact, a chocolate layer cake with chocolate mousse filling, frosted with a chocolate buttercream, then topped with a chocolate ganache.  And for good measure, an added  garnish of chocolate covered bits of Rice Crispies.

Definitely a new standard in chocolate overload.  The family loved it and I think you will too.

And just in case this isn’t enough chocolate to keep you occupied, my middle son’s birthday is tomorrow.  Guess what he’s requested?


<img alt="Valhrona Chocolate Bar"/>

Four Layer Chocolate Mousse Cake

Printable Recipe

Cake Batter Ingredients

1/2 c. unsalted butter

1-1/3 c. extra fine sugar

1/2 c + 2 T unsweetened cocoa powder

2 lg. eggs

2 oz unsweetened chocolate, melted

1-3/4 c. flour

1 tsp. baking powder

3/4 tsp. baking soda

1/4 tsp. salt

1/2 c. water

1/2 c. whole milk

Chocolate Mousse Ingredients

8 oz. semi sweet chocolate

1/2 c. unsalted butter

4 lg. eggs

6 T extra fine sugar

2 T water

2/3 c. heavy cream

Chocolate Buttercream Frosting Ingredients

1-1/4 c. heavy cream

8 oz. semisweet chocolate, chopped

1/2 c. unsalted butter

1/2 tsp. vanilla

1/4 c. powdered sugar

Chocolate Ganache Ingredients

4 oz. semi sweet chocolate, chopped

1/2 c. heavy cream

3 T light corn syrup

1 T canola oil

1/2 tsp. vanilla

Chocolate Covered Crispy Garnish Ingredients

1 cup Rice Crispies cereal

2 oz. semi sweet chocolate


<img alt="Chocolate Cake Mise en Place"/>

<img alt="Cooling Chocolate Cake Layer"/>


At least one day before serving, make the chocolate cake.

  1. Prep all ingredients for the cake batter, making sure they’ve at room temperature before beginning.  Preheat oven to 325°F and position a rack in the center of the oven.  While you’re waiting, spray a 9-inch round cake pan with oil, line the bottom of the pan with parchment and spray it lightly.
  2. To make the cake batter, melt the chocolate either slowly over very low heat on the stove, or in the microwave using 20 to 30 second intervals, removing, stirring, then returning for 15 seconds at a time to repeat: stir, heat, stir, heat until the chocolate is completely melted.  Allow to cool to a tepid temperature so it is ready to use.
  3. Sift the flour, baking powder, baking soda, and salt together in a bowl and set aside until ready to use.
  4. In a large mixing bowl, cream the butter with the sugar and cocoa powder on medium high until mixed well.  It will have a grainy appearance.
  5. Add the eggs, one at a time, running the mixer until each is incorporated.  Make sure to scrape the sides and bottom in between and after mixing in the eggs.
  6. When the melted chocolate is cool enough that it will not melt the butter, add it to the mix and blend it in.  The batter should be smooth.
  7. Heat the milk with the water until hot — but not so hot that you cannot keep your finger in it when you test it.  Set aside.
  8. Add the dry ingredients to the mixing bowl and slowly incorporate them just until completely blended.
  9. With the motor running on slow, pour in the hot milk then increase speed to medium to completely mix.  Scrape down the sides of the bowl and mix briefly to blend everything together.
  10. Pour the batter into the prepared cake pan and place in the preheated oven for 40 minutes, or until a wooden skewer inserted into the center is removed clean.  The cake will have pulled away from the sides of the pan only slightly.  Allow to cool completely on a baking rack before removing it from the baking pan.  Wrap it with plastic wrap and place in the fridge until chilled.

<img alt="Chocolate Mousse Ingredients"/>

<img alt="Whipped Egg Whites"/>

<img alt="Making Chocolate Mousse"/>

Make the chocolate mousse after the cake is completely chilled.

  1. Once the cake is wrapped and in the fridge, begin the chocolate mousse by melting the chocolate and butter together either on the stove, over very low heat, or in the microwave as previously described, in short intervals, stirring at the end of each before continuing.  When the mixture is completely smooth and glossy, scrape into a large bowl and set aside.
  2. In a clean bowl, mix the heavy cream just until it comes together and whip lines are slightly visible.  Set in the fridge to keep chilled.
  3. Over a pan of simmering water, place a heat resistant bowl (or use a double boiler).  Add the eggs, sugar, and water, and heat, whipping until frothy, pale in color and warm to the touch.
  4. Once warm, pour the mixture into a clean mixing bowl and mix on high for 3 minutes.  The mixture should be very thick, smooth, and nearly white in color when finished.
  5. Scoop about 1/3 of the egg mixture into the melted chocolate, and using a folding motion, lightly blend the two.  There will still be streaks of light and dark in the mixture.
  6. Then add the rest of the egg mixture to the lightened chocolate mixture, carefully folding until a fairly uniform tone.
  7. Add the whipped cream and lightly fold that in as well taking care not to deflate the egg whites.
  8. Place the mousse in the fridge until the cake is prepped.

<img alt="Split Chocolate Cake Layer"/>

My layers aren’t exactly even…not even close!

<img alt="Making a 4-Layer Chocolate Mousse Cake"/>

The first layer of mousse goes over the first cake layer.

<img alt="Making a 4-Layer Chocolate Mousse Cake"/>

I almost tore the layer getting it in the pan!

<img alt="Final Mousse Layer"/>

Assemble the cake a minimum of 6 hours before serving time.

  1. Very lightly spray a 9-inch springform pan with oil and line it with parchment.
  2. Remove the cake from the fridge and using a very long, sharp knife, slice it through its middle to create two layers of equal size.
  3. Carefully place one layer into the bottom of the sprinform pan making sure it’s snug.
  4. Remove the mousse from the fridge and spread half over the cake layer, making sure to even it out to the edges.
  5. Now add the second layer of cake and place if over the mousse.  Gently press.
  6. Spread the remaining mousse over the second cake layer, again spreading to even it out.
  7. Place the cake in the freezer for at least 4 hours.
  8. Once the top of the cake is firm to the touch, cover it in plastic if it will be in the freezer overnight.

<img alt="Frozen Chocolate Mousse Cake Layers"/>

Make the buttercream frosting just after putting the assembled cake into the freezer.

  1. In a pan over medium heat, bring the cream to a boil then pour it over the chopped chocolate.  Let it sit for 2 minutes before stirring until completely blended.
  2. Place it in the fridge for a minimum of 3 hours.
  3. Just before the chocolate cream mixture is ready to be removed from the fridge, cream the softened butter and vanilla in a mixing bowl on medium until smooth.
  4. Add the chilled chocolate cream mixture (it should be the consistency of peanut butter) and powdered sugar.  Using a whip attachment, mix on medium high for 3-4 minutes until fluffy.
  5. Chill until ready to use.

Once the cake and mousse layers are finished in the freezer, the cake is ready to be frosted.

  1. Remove the springform pan from the freezer.  Run a thin knife smoothly around the edge of the pan to help release it.  If necessary, use a hair dryer to warm the edges of the pan slightly before slowly releasing the tension on the pan.   Remove the cake from the pan.
  2. Prepare the cake plate you will serve the cake on by lining it with pieces of parchment to be removed after frosting.  Remove the cake from the bottom of the cake pan (the cake will be quite firm), then peel off the parchment from its bottom.
  3. Place the cake on the prepared cake plate.
  4. Spread thinly with the chilled buttercream.
  5. Place in the fridge while the chocolate ganache and garnish are prepared.

To make the chocolate ganache topping

  1. Heat the heavy cream, corn syrup, and oil until just before boiling either over the stove or in a large bowl in the microwave for about 45 seconds.  Stir to blend, then pour the mixture over the chopped chocolate.
  2. Allow to sit for 2 minutes, then mix well until everything is smooth and glossy, then add the vanilla and mix well.
  3. To use immediately, remove the cake from the fridge, pour the ganache over the surface of the cake and with an offset spatula, quickly smooth across the surface of the cake, allowing some to dribble down the sides.
  4. If making the ganache ahead, place in the fridge in a covered container.  When ready to use, heat in the microwave to bring to a pourable consistency and proceed.
  5. Once the ganache is on the cake, place the cake back in the fridge

<img alt="Chocolate Covered Rice Crispies"/>

Make the chocolate covered crispy garnish

  1. Melt the chopped chocolate as described above, either by heating over a very low flame, or in the microwave in 30 second intervals, stirring in between.
  2. When the chocolate is completely melted, pour the cereal in and using a spatula, gently toss to completely cover it in chocolate.
  3. Line a baking pan with parchment and spread the chocolate crispies over it, making sure that there are clumps attached here and there.
  4. Place in the fridge to harden.
  5. When set, decorate the top of the cake however you wish.

<img alt="Four Layer Chocolate Mousse Cake"/>

Serving the cake

  1. If the cake has not been out of the freezer long, make sure it has ample time in the fridge to thaw before serving.  Leaving it at room temperature for a while before serving won’t bother it too much.
  2. Use a warm knife to slice through.
  3. Serves 16-20.

<img alt="Chocolate Covered Rice Crispies Cake Garnish"/>

<img alt="Four Layer Chocolate Mousse Cake"/>

Recipe Notes

  • This cake was adapted from the Quadruple Chocolate Cake recipe found at Pastry Pal who sadly appears not to be writing any longer.  A shame — such a talent!  And she provides far more detailed step-by-step photos than I have here, so by all means, check them out.  I’ve tried to make the directions flow more effectively, but just followed my own prep process.  You may have one entirely different!
  • Yes, this recipe has many, many steps.  But you know I’m all over that.  This is one of those “all good things in time” recipes that truly looks and tastes as if it came from a high end pastry shop.  It’s delicious and has intense chocolate flavor without an over the top sweetness that will always kill a dessert for me.  We loved this.
  • I highly recommend starting this cake at least one day in advance — the morning of a day in advance.  The cake needs to chill thoroughly, then the mousse filled layers need to freeze at least 4 hours.  The frosting has to chill at least 3 hours.  So it would be easy to make the cake one morning, cool it.  Then split it and fill it later in the day to let freeze overnight.  Make the frosting either just before calling it a night.  First thing the next morning, the rest comes together quickly and the cake still has time in the fridge to continue its thaw.
  • If you’ve made mousse before, then the technique is the same — there isn’t anything new other than perhaps minor changes with ingredient quantities than what you may have used before.  The key to making mousse is to not deflate the egg whites!  Good folding technique is something to have here.
  • I have to say the cake baked beautifully in this recipe.  It’s a great all round chocolate cake recipe that could be used for many things.  The crumb is even and firm — perfect for the mousse.  Anything lighter, or fluffy could end up soggy with the mousse layers.
  • My layers weren’t cut evenly because I didn’t want to slice off the top of that cake.  I know I should, but I never do.  Tsk. Tsk.  So no, I do not have perfect layers.  It it didn’t affect the taste one bit.
  • The trickiest part of making this was getting the cake layers into the springform pan to begin the mousse layering without tearing them.  I almost did.  But even so, you would be able to piece it back together and the mousse would hold everything well.
  • The only question I have about this entire recipe is with the frosting.  Only a very small quantity is made — that’s fine.  Spread more on the sides than the top since you’ll pour over the ganache.  But I had some trouble with the ingredients holding together.  I’m used to making buttercream with a mousselline or Italian meringue technique.  I never make it with just butter and powdered sugar.  And to be fair, I did not use milk chocolate, so…All was fine in the end, but I had to do a lot of patching.  Since the cake is very cold, the butter in the frosting hardens fairly quickly, so I used an offset spatula dipped in warm water to smooth things out.  It worked, but I’m still not sure what I did to prevent a smooth, fluffy frosting.  I tried to pipe a decorative border as shown in the original recipe, but the frosting was almost separating and wouldn’t pipe properly.
  • I need lessons for artfully allowing a topping to dribble over the sides of a cake.  I truly do.  I was worried that if the ganache was too warm, it would melt the buttercream — or worse, the mousse immediately below.  So I sacrificed by going on the cooler side and as soon as it hit that cake, it started to thicken, of course.
  • Because I couldn’t make a decoration, I added the Rice Crispy pieces as an afterthought.  I saw them on the Pastry Pal site again after trying to decide between this cake and another fabulous dessert.  Make sure the chocolate you use is sweet enough for these.  Otherwise, they’re SO tasty, I had trouble not just snacking on them.  They will get soggy after a while sitting on this cake, but I understand they keep quite a long time in the freezer if wrapped well.  Definitely a keeper recipe for those — and they’re fun and easy to work with!
  • What adaptations did I make to this recipe?  Mostly with brands & types of chocolate.  I used what I had on hand which was a collection of unsweetened Ghirardelli, Valrhona semisweet, and Sharfen-Berger bittersweet chocolate. When I don’t have the kind of chocolate called for in a recipe, I look for substitutions mostly having to do with adding sugar to dark chocolate.  The Ghirardelli site has them here. I also used extra fine sugar and a French Brandy vanilla I make myself.
  • If I made this cake again, I would make three layers of cake with mousse layers in between for a couple of reasons.  First, I like the idea of a cake layer being on top.  Second, it would give the cake some extra height.  I like a nice, tall cake.  I would also either double the frosting recipe and perhaps add the ingredients differently (add the butter a tablespoon at a time, beating as I go) or just use a different frosting recipe.  On the other hand, I could just make it as directed with the milk chocolate.

<img alt="Four Layer Chocolate Mousse Cake"/>