Every time I flipped through Pierre Hermé’s Desserts, there are just tonnes of recipes I wanted to try out – it is impossible to pick just one. But, unfortunately, time is a limit, so is the capacity of my freezer. So for this special week 100, I decided to pick a rather basic, but delicious creation, the Mocha cake. Light layers of coffee génoise, smothered by coffee syrup, sandwiching rich mocha pastry cream, and covered by a delicious coffee buttercream. Mmm.
As usual, I adapted the recipe to make a 6-inch cake. And I also had to substitute some of the ingredients I couldn’t find, and some that is just too difficult to half. The resulting cake turned out absolutely scrumptious, so there.
Makes a 6-inch round cake
For the coffee génoise
150g eggs (roughly 3 medium)
100g caster sugar
5g instant coffee
15g coffee extract
100g plain flour
1) Preheat convection oven to 190C. Grease a line a 6-inch round cake tin with removable bottom.
2) In the bowl of a stand mixer, over a bain-marie, gently heat the eggs and sugar, whisking continuously until the temperature is between 55C and 60C.
3) Transfer the mixing bowl to a stand mixer, and using the whisk attachment, beat on high speed until egg mixture is pale and thick, and has cooled down to room temperature.
4) Dissolve the instant coffee in the water. Then add the coffee syrup and stir to mix.
5) Scoop 2 tablespoons of the egg mixture into the coffee mixture and whisk to lighten. Then, pour the coffee mixture into the egg mixture carefully on the edge of the mixing bowl.
6) Sift half the plain flour into the egg mixture and fold lightly. Then sift the other half of the plain flour in, and fold until there are no streaks.
7) Pour cake mixture into the prepared cake tin and bake in preheated oven for 20 to 25 minutes until a tester inserted into the middle of the cake comes out clean.
8) Allow to cool slightly, then remove cake from the tin. If you are not using immediately, wrap the cake in cling wrap and freeze.
For the coffee syrup
35g caster sugar
10g instant coffee
1) Add 37g water to the caster sugar in a heavy bottom saucepan and allow to boil until sugar is dissolved. Remove from heat and allow to cool.
2) Dissolve the instant coffee in the remaining water and stir into the cooled syrup.
3) Add Kahlua into the syrup and stir well. You can adjust the amount of Kahlua based on your preference.
For the pastry cream
1/4 tsp vanilla bean paste
125ml whole milk
30g caster sugar
30g egg yolks (roughly 2 medium)
15g unsalted butter, at room temperature
1) In a heavy-bottomed saucepan, heat the vanilla bean paste and whole milk until it started boiling around the edge of the saucepan.
2) Whisk the caster sugar, cornstarch and egg yolks in a bowl. Then, pour the hot milk mixture into the eggs slowly to temper it.
3) Pour the tempered eggs back into the saucepan and continue cooking, whisking continuously until mixture has thicken.
4) Remove from heat and plunge bottom of saucepan into cold water to stop the cooking process.
5) When it was cooled to about 60C, add the room temperature butter and whisk until butter is incorporated.
For the lightened mocha cream
40g heavy cream
5g instant coffee
10g dark chocolate couverture (> 70% cocoa)
32g unsalted butter, at room temperature
Pastry cream from above
1) Whisk the heavy cream using a hand mixer until stiff. Refrigerate.
2) Dissolve instant coffee in water, then, add the dark chocolate couverture, and heat on a bain marie until chocolate is melted. Stir the mixture well.
3) Cream the butter until it is light and fluffy. Add the pastry cream and coffee mixture and continue to beat until combined.
4) Fold in the whipped cream.
For the coffee buttercream
35g caster sugar
100g very soft unsalted butter
7g room temperature water
2g instant coffee
7g coffee extract
1) In a saucepan, bring the 13g water and sugar to a boil. Cook the syrup until it reaches a temperature of 120C.
2) In a bowl, using a hand mixer, whisk the eggs until light and pale. Gradually our the hot syrup down the side of the bowl, avoiding the whisk. Continue whisking until egg mixture has cooled down to room temperature.
3) In the bowl of a stand mixer, beat the butter using the whisk attachment until creamy. Gradually incorporate the egg mixture and whisk until buttercream is smooth.
4) Dissolve the instant coffee in the remaining water, then add the coffee extract and stir well.
5) Pour coffee mixture into the buttercream and allow to whisk until buttercream is light and fluffy.
75g toasted and chopped hazelnuts
Cocoa powder and chocolate coated coffee beans to decoate
1) Slice the coffee génoise horizontally into 3 equal layers
2) Place the first layer onto a cake board. Using a pastry brush, brush the top of the cake generously with coffee syrup. Then top with half the lightened mocha cream.
3) Place the second layer of génoise on top of the mocha cream and press down lightly.
4) Repeat with syrup and remaining mocha cream. Then place the last layer of génoise. Brush the top of the cake with coffee syrup then allow to freeze for an hour.
5) Remove cake from freezer, and cover the top and sides of the cake with coffee buttercream.
6) Coat the sides of the cake with chopped almonds. Refrigerate the cake for an hour to allow the buttercream on top of the cake to harden.
7) Remove cake from refrigerator and sprinkle the top of the cake with cocoa powder. Then, pipe a border along the top edge of the cake with the remaining buttercream. Finally decorate with chocolate coated coffee beans.
For the cocoa powder decoration, I cut out a checker-board patter on a piece of A4 paper, place it on top of the cake when the buttercream is cold, and sift cocoa powder onto the stencil to get the pattern. I was worried I wouldn’t have enough buttercream to decorate the cake, but, it was enough, with a little extra.
Pierre Hermé recommends letting the cake sit in the refrigerator for 2 days to allow the cake to soak in all the flavours from the syrup, pastry cream and buttercream. For me, that is probably the hardest part of this recipe.