Preheat the oven to 200 C / Gas 6. Line a baking tray or springform tin with greaseproof paper and butter the paper.
Separate eggs. Beat the egg yolks and vanilla with 2/3 of the sugar with an electric mixer until creamy.
In another bowl, beat egg whites with the remaining sugar until stiff. Add to the yolk mixture.
Mix flour, cornflour and baking powder and sift into the egg mixture. Fold everything thoroughly but carefully together with a spatula.
Pour the mixture into the tin and even it out with a spatula. Bake in the preheated oven for 25 minutes.
Remove the sponge from the cake tin. Carefully remove the baking parchment. Cool on wire rack.
For the chocolate mousse filling, heat the cream with the chocolate and coffee granules until everything has dissolved. Mix well and leave to cool. Place in the refrigerator overnight.
Bring the raspberries and sugar to the boil. Mix the cornflour with water and add to the raspberries. Bring to the boil while stirring constantly until the mixture is clear again, about 5 minutes. Allow to cool.
Cut sponge horizontally into 3 equally thick layers. Spread the raspberry filling over the bottom layer. Place the second pastry layer on top.
Beat the chocolate mixture and whipped cream stiffener until stiff. Spread about 1/3 of it over the second pastry layer. Place the third layer on top and cover the top and sides of the cake with the remaining chocolate mixture. Refrigerate the cake until serving.
Whip It® whipped cream stiffener is available in German speciality stores and online.