Dark Chocolate Mousse Layer Cake

This is an adaptation of Sally’s excellent recipe on Sally’s Baking Addiction. I made this for my father-in-law. This is adapted for Australian ingredients and metric units.

This is an impressive cake! It has layers, sweetness, and a “wow” factor that’s hard to beat. It isn’t cheap to make — it’ll cost around $20 in ingredients (all that chocolate and cream) — but its value is at least $100.

The cool thing is it’s not too hard to make. It just takes time. I’d say it’s “intermediate” level. Yes, you have to know how to make a mousse and how to make a ganache. But if you can do those, or if you can figure it out, then you’re fine.

Generally, make this cake over two days. You could do it all from the morning of the day you’re going to serve it, but that might cause unnecessary stress.

General disclaimer: I’m not a food blogger, so these are personal notes. The outcomes are amateurish. Go to Sally’s blog for the original stuff, especially if you’re American, as the quantities and ingredients will be most relevant there.

Tools Required

• Mandatory: At least two 8-inch or 9-inch round cake pans (bake in two sets). If you have four tins and a huge oven, go ahead and use all four!
• Preferable: Large icing spatula + Bench scraper. (You can just use a rubber spatula if needed)

Ingredients & Shopping List

The below ingredients are slightly modified. There’s a bit less sugar, and darker chocolate.

Core things to get on the shopping list (aside from what you probably have in the pantry) are

• Duch-process cocoa powder
• Cream (you need about 750 ml; two cups for the mousse, and one for the ganache)
• Chocolate chips (you’ll need three small bags as you need 675g total)
• Buttermilk
• Sour cream

Cake Layers

These are the ingredients for four cake layers (or three slightly bigger ones).

• 1 and 3/4 cups all-purpose flour
• 3/4 cup dutch-processed cocoa powder
• 1 and 3/4 cups granulated sugar
• 2 teaspoons baking soda
• 1 teaspoon baking powder
• 1 teaspoon salt

Wet ingredients must be at room temperature.

• 1/2 cup vegetable oil
• 2 large eggs
• 3/4 cup sour cream
• 1/2 cup buttermilk
• 2 teaspoons vanilla extract
• 1/2 cup fresh brewed coffee (using high-quality, freshly ground beans; don’t use instant)
• 1 cup dark chocolate chips

Chocolate Mousse

• 1/2 cup hot water
• 1/4 cup dutch-processed cocoa powder
• 225g dark chocolate chips
• 2 cups pure cream or thickened cream
• 2 tablespoons icing sugar
• 1/2 teaspoon vanilla extract

Chocolate Ganache and Garnish

• 225g dark chocolate chips
• 1 cup heavy cream
• Fresh strawberries

Instructions

Prepare the cake layers and mousse the day before. Refrigerate overnight, then assemble and pour the ganache the following day (at least 2 hours before serving).

Day before: Bake cake layers

1. Preheat oven to 180°C. Grease and line two cake pans with parchment paper. Grease the parchment as well.
2. In a large bowl, whisk together flour, dutch-processed cocoa powder, sugar, baking soda, baking powder, and salt. Set aside.
3. Using a mixer or whisk, mix oil, eggs, and sour cream on medium speed until combined.
4. Add buttermilk and vanilla extract, mixing until fully incorporated.
5. Slowly combine wet and dry ingredients, then mix in the coffee. Ensure batter is smooth.
6. Fold in chocolate chips.
7. Divide the batter evenly between the two pans. Bake each set for 20-25 minutes, or until a toothpick inserted in the centre comes out clean.
8. Cool the cakes completely in their pans on a wire rack.

Day before: Prepare chocolate mousse

1. Whisk hot water and cocoa powder together. Set aside.
2. Melt chocolate chips using a microwave (stirring every 20 seconds). Stir the cocoa mixture into the melted chocolate until smooth.
3. Whip cream, icing sugar, and vanilla extract on medium-high speed until medium peaks form (about 3-4 minutes).
4. Fold in the chocolate mixture gently until combined. Chill for at least 2 hours or up to 2 days.

Night before / Morning of day of serving: Assemble cake

1. Place one layer on a serving plate. Spread 1.5 cups mousse evenly on top.
2. Repeat with the second and third layers, reserving a small amount of mousse for a crumb coat.
3. Use the remaining mousse as a crumb coat and smooth with a bench scraper. Chill the assembled cake for 1-4 hours.

At least 2 hours before serving: Make and apply ganache and garnish

1. Heat cream in a microwave (do not boil)
2. Pour over chopped chocolate and let sit for 2-3 minutes. Stir until smooth.
3. Cool at room temperature for 20 minutes before pouring over the chilled cake.
4. After it has cooled, pour ganache over the cake, smoothing with an icing spatula.
5. Garnish with fresh strawberries.
6. Chill for 2 hours before serving.

How it came out

The first time I made this, there was a panoply of errors.

• I only had one cake tin. I made it in a cake tin + a pot, which had a slightly different diameter.
• Two of the cake layers stuck to the tins. One of them fell out and crumbled to pieces (I reassembled it)
• The oven’s dial had most of the numbers rubbed off, and was leaky — I didn’t really know what temperature it was at!
• My mother-in-law chopped up the strawberries for a smoothie before she realised I wanted to use them for decoration

So, some of the layers fused, and it was very hard to get the exterior looking good. Ganache covers all issues, though.

Despite all that I got it together. Of course, it was delicious, notwithstanding the errors.