Combine flour, sugar, cocoa and baking powder with salt. In another bowl beat together egg yolks, water,and oil.
Beat the egg whites until stiff. Mix liquid with flour mixture and carefully fold egg whites in.
Preheat oven to 165C and line 20cm baking form with baking paper. Divide the batter in two parts and bake separately for about 25 minutes. Let them cool.
For the cream heat milk. Mix flour, sugar and yolks in a separate bowl and add some of the warm milk to it to dissolve.
When milk begins to boil pour flour mixture into milk and stir all the time until it thickens. Set aside, add coffee and chill it. Beat butter, sugar powder and coffee cream until pale.
For ganache: melt chocolate chunks and chopped butter in the microwave. Stir and chill in the fridge until it has hardened.
Whip chocolate ganache until lightened in colour.
Trim cake edges and sandwich two cakes with coffee cream. Cover sides of the cake as well. Let it rest in the fridge for a while. Sprinkle with cocoa powder onto the sides of the cake (I used my fingers to help spreading cocoa powder evenly over chilled butter cream