For the cake: In a large bowl, beat together egg yolks, sugar and vanilla until light and creamy.
In another bowl, beat egg whites until stiff. Fold into the melted chocolate.
Choose a mould like a souffle dish, coat with flour and pour in the batter. Bake in preheated oven for 30-40 minutes (a knife should come out clean). Remove from dish and cool.
For the syrup: Add sugar and 1 tablespoon water in a saucepan. Heat until it starts to bubble. Stir in Kirsch and leave for 1 minute, then remove from heat.
Slice the cake into three horizontal pieces using a large serrated knife. Separate the pieces and soak each piece in 1/3 syrup. Let cool.
For the buttercream: Beat butter and sugar until smooth. Add eggs yolks and Kirsch. Beat until smooth and creamy. Set aside.
In another bowl, whip double cream with 2 teaspoons sugar. Set aside.
To assemble: Transfer one slice of cake to a serving plate. Spread with 1/2 buttercream. Layer 1/2 cherries on top, then cover with 1/3 sweetened cream.
Arrange the second sponge cake layer on top. Spread with remaining buttercream. Layer cherries on top, then with 1/3 cream.
Arrange the third sponge cake layer on top. Spread remaining sweetened cream on top. Decorate with cherries and chocolate shavings. Refrigerate for at least 1 hour (or maximum of 48 hours before serving).