Sieve the flour and baking powder twice. Beat the eggs and sugar till the stip point, add the vanilla essence. Finally, add the cocoa and flour mixture to the egg mixture gradually. Preheat your oven, pour the batter in a lined baking tin and bake at 200° C for 25 minutes. Let the cake cool, cut it into pieces. Cream the butter and icing sugar, add cocoa powder then apply the chocolate cream into pastry pieces. Keep it in the fridge for 30 minutes for the set then serve it.