For the mousse, bring cream and coffee beans to the boil, remove from the heat and allow to steep for about 5 minutes. Break the milk chocolate into pieces. Pour cream through a sieve into another pot and heat it up.
Melt chocolate in it. Pour into a mixing bowl and cover directly on the surface with cling film. Allow to cool slightly, then place in the refrigerator for at least 4 hours, preferably overnight.
Preheat oven (electric cooker: 175 °C/circulating air: 150 °C/gas: see manufacturer). Grease the bottom of a springform pan (26 cm Ø) and dust with flour. For the sponge cake, chop the dark chocolate coating coarsely. Melt in a hot water bath and let it cool down for about 5 minutes.
Separate eggs. Beat the egg whites and 5 tablespoons of cold water with the whisks of the mixer until stiff, gradually adding 1 pinch of salt, sugar and vanilla sugar. Whisk the egg yolks and stir into the beaten egg white.
Add the liquid chocolate coating while stirring. Mix flour, 25 g cocoa and baking powder, sieve onto the egg foam and carefully fold in.
Pour the sponge mixture into the springform pan and smooth it down. Bake in a hot oven for 20-25 minutes. Let the sponge cake cool down in the tin on a cake rack. Remove the sponge cake from the tin and cut through horizontally once.
Whip the chocolate cream with the whisks of the mixer until thick and creamy. Spread approx. 2⁄3 of the cream on the lower base. Place the second base on top. Add the rest of the chocolate cream and spread loosely.
Chill for about 2 hours. Just before serving, dust with 2 tablespoons of cocoa.