First flour and cocoa sifted, put in a deep bowl, add salt and mix. Second - in a bowl pour softened margarine and sugar, stirred with a mixer at low speed about 2-3 minutes and added one by one egg after each stirring lasts about 2 minutes. Third - little by little to the margarine and sugar are added flour-cocoa mixture and mixed with soda sour milk alternately. Stir at low level of about 5 minutes and was flavored with vanilla flavor. Fourth - the mixture is poured into a tray covered with baking paper in the desired form. Bake about 20-30minuti at 160-180 degrees. For the cream: Beat eggs, sugar, flour, salt and 100 ml milk to obtain cream. Rest of the milk boil. The hot milk is poured in a thin stream to the cream until homogeneous. Then pour into a clean container and boil to thicken (cream stirring constantly). Withdraw cream from the heat and add the butter and chocolate, then beating until melted. The bases halve on each applied layer of cream. Optional decorate and leave to stand for several hours before serving.