Coffee Gianduja Chocolate Mousse Cake

** The post was updated and revised in a new post with a more pronounced coffee flavor, an espresso brownies base and a better preparation method. You can find the update in this link **

It’s not every day you celebrate a birthday. It’s not every day you eat a birthday cake. A festive event calls for a festive cake. And what’s more festive than brownies with hazelnuts, topped with a layer of dark chocolate & coffee mousse, topped with a second layer of gianduja chocolate mousse. Three layers of pure joy.

I made this mousse cake for my dear friend’s birthday (happy birthday Sumaya!). It was a surprise party.. And oh how I love surprises! Some people might say I remind them of Sue from SNL.

It’s funny to think that I’ve never had my own surprise party that surprised me completely. The last one almost succeeded, but it got ruined 2 minutes before the actual “surprise” shout, unintentionally, by that same friend! I had the opportunity to get back at her when I was invited to her surprise birthday party, but decided against it. Revenge is sweet, but this mousse cake is much sweeter.

I found the inspiration for this cake on the blog “Savor The Best“. The recipe and the technique are a little bit different here. Be warned, this mousse cake is very rich and may be heavy to eat as a dessert after a big meal (or snacking on it endlessly at a party, ehm). Personally, I would give up lunch and just eat a slice of this mousse cake instead.

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Ingredients

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Brownies with hazelnuts
2 eggs
130 g sugar
180 g dark chocolate
130 g butter
2 tsp instant coffee in granules
1 tsp vanilla paste
1 tbsp boiling water
40 g self-rising flour
60 g chopped hazelnuts

Gelatin mass
12 g gelatin powder
60 g water

Chocolate coffee mousse
90 g egg yolk
40 g eggs
65 g sugar
45 g water
30 g gelatin mass
360 g dark chocolate
300 g heavy cream
3 tbsp instant coffee in granules

Gianduja chocolate mousse
90 g egg yolk
40 g eggs
65 g sugar
45 g water
40 g gelatin mass
165 g chocolate milk
165 g praline paste
30 g dark chocolate 70%
4 g cocoa butter
300 g heavy cream

Decoration
Some cocoa nibs

Equipment
A round ring with, 23 cm diameter and 10 cm height
Acetate strip, 10 cm height

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Advance prep

Gelatin mass:  Sprinkle gelatin powder over the water, mix well and keep in the fridge for at least half an hour. Cut into small pieces before use.

Cream infusion (for the chocolate coffee mousse): The goal here is to give the heavy cream a coffee taste before whisking it. This can be done in two ways:

• Cold infusion: Pour heavy cream into a bowl. Add coffee granules and mix a little. Cover with plastic wrap and keep in the fridge for a night (about 12 hours). Mix well before use.
• Hot infusion: Put a quarter of the heavy cream in a kettle and add the coffee granules. Start warming on medium heat, while mixing all along, only until the coffee melts. Transfer to a bowl and add the rest of the cream. Mix well. Keep in the fridge for at least two hours so that the cream is cold enough before whisking.

Brownies with hazelnuts

Place a layer of aluminum foil on a baking tray, followed by a layer of parchment paper and topped with the ring. Fold the edges of the paper and foil to the sides of the ring and tighten them so that the batter won’t spill out of the bottom of the ring. Lightly grease the inner wall of the ring and line it with parchment paper. Set aside.

Preheat the oven to 180 °C (350 °F). Put eggs and sugar in the mixer bowl and whisk until you get a thick, light texture (make sure to scrape the sugar at the bottom of the bowl).

Melt the chocolate and butter on a double-boiler, while mixing all along, until the mixture is smooth and uniform. Put coffee granules and vanilla in a cup, add boiling water and mix until combined. Add the chocolate mixture to the egg mixture. Add the cup of coffee as well and mix until uniform. Fold the flour into the batter. Add hazelnuts and mix just a bit.

Pour the batter into the ring and flatten the surface with a spreading spatula. Place the tray in the oven and bake for 30-35 minutes until the top of the brownies is firm to the touch. Let the brownies cool at room temperature. Release the ring, remove the parchment paper and place the brownies on a serving plate. Wash the ring, dry it and place it around the brownies, with an acetate sheet in between.

Chocolate coffee mousse

Remove the coffee infused heavy cream from the fridge and whisk until you almost get soft peaks (beware not to over whip, the goal is to get a texture that resembles yogurt). Keep in the fridge.

Melt the chocolate on a double-boiler. Once the chocolate has melted, turn off the flame and leave the bowl on the double-boiler (the goal is to keep the chocolate warm around 50 °C (120 °F) before combining with the eggs).

Put water and then sugar in a saucepan. Place on medium heat. Stir the sugar with a spatula to dissolve it. Once the water starts to boil, stop stirring and remove the spatula. Let the syrup boil and check with a thermometer that the temperature does not exceed 115 °C (240 °F). While it’s boiling, whisk the eggs and the egg yolk together in a mixer on high speed.

As soon as the syrup reaches 115 °C (240 °F), turn off the stove, reduce the mixer speed to medium, and slowly pour the syrup into the mixer. Increase the mixer speed to high and continue to whisk for about 5 minutes, until the egg mixture cools. When you drop a spoonful of the mixture into the bowl it should fall back in ribbons and disappear into the mixture slowly. In the meantime, melt the gelatin mass on a double-boiler.

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Add the melted gelatin mass to the egg mixture and mix a little. Add the warm chocolate and mix until uniform. The texture will become viscous.

Remove the heavy cream from the fridge and whisk it a little more (remember, yogurt texture). Fold the heavy cream into the egg mixture in three parts. Pour immediately into the ring over the brownies. Give it a little shake to flatten the mousse and keep it in the freezer for about an hour or two.

Gianduja chocolate mousse

Whisk the heavy cream until you almost get soft peaks (beware not to over whip, the goal is to get a texture that resembles yogurt). Keep in the fridge.

Melt milk chocolate, dark chocolate and cocoa butter on a double-boiler. Once the chocolate has melted, turn off the flame. Add the praline paste and mix until uniform. Leave the bowl on the double-boiler to keep the mixture warm.

Put water and then sugar in a saucepan. Place on medium heat. Stir the sugar with a spatula to dissolve it. Once the water starts to boil, stop stirring and remove the spatula. Let the syrup boil and check with a thermometer that the temperature does not exceed 115°C (240°F). While it’s boiling, whisk the eggs and the egg yolk together in a mixer on high speed.

As soon as the syrup reaches 115 °C (240 °F), turn off the stove, reduce the mixer speed to medium, and slowly pour the syrup into the mixer. Increase the mixer speed to high and continue to whisk for about 5 minutes, until the egg mixture cools. When you drop a spoonful of the mixture into the bowl it should fall back in ribbons and disappear into the mixture slowly. In the meantime, melt the gelatin mass on a double-boiler.

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Add the melted gelatin mass to the egg mixture and mix a little. Add the warm chocolate and mix until uniform. The texture will become viscous.

Remove the heavy cream from the fridge and whisk it a little more (remember, yogurt texture). Fold the heavy cream into the egg mixture in three parts. Pour immediately into the ring over the chocolate coffee mousse. Give it a little shake to flatten the mousse and keep it in the freezer for at least two hours (and even more – It’s easier to remove the acetate strip without affecting the form of the cake when it’s frozen solid).

After the mousse has set in the freezer, release the ring and peel off the acetate strip. Decorate the top of the mousse cake with cocoa nibs. Keep in the fridge (or in the freezer for an extended shelf life. However, don’t forget to let it defrost in the fridge for at least 2 hours before serving).

Yum