Mix flour and sugar. Heat 250 g fat, 4 tablespoons cocoa and 350 ml cola in a saucepan, bring to the boil briefly. Pour over the flour mixture and mix with the whisk of the hand mixer. Whisk buttermilk, eggs, baking powder and vanillin sugar. Add to the cola mixture and mix everything thoroughly. Grease a rectangular form (approx. 21 x 30 cm) and dust with flour. Add the dough and smooth it down.
Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for 35-45 minutes. Remove the cake. Heat icing sugar, 1 tablespoon of cocoa, 25 g fat and 2 tablespoons of cola in a saucepan while stirring until smooth. Put the icing on the still hot cake and spread it. Let it cool down. Cut the cake into pieces and decorate with chocolate rolls
2 hours waiting time