Mash the cake with milk in the mixing bowl until dough forms.
Place the cake dough on a sheet of plastic food wrap and cover with another sheet of plastic food wrap. Flatten the cake with cake roller (approximately 1 cm thick).
Beat the whipping cream with cocoa powder until stiff peak form. Spread the whipped cream over the cake.
Roll up the cake, cover with plastic wrap and keep in the fridge for 2 hours.
Melt cooking chocolate with microwave oven or “double-boil”. Gradually pour in whipping cream and milk, stir until well combined.
Slowly pour the chocolate ganache over the top of the cake. Let the ganache set before cutting.
Tip: For smoother cake texture, use only the inner part of cake (discard the top, the bottom and the sides of the cake).