Cream fat, sugar and salt with the whisk of the hand mixer. Stir in the eggs one after the other. Mix flour and baking powder, alternately stir in 1/4 litre milk into the fat egg mass. Halve the dough. Cut the chocolate mint bars into small pieces.
Stir cocoa, mint bars and 4 tablespoons of milk into one half of the dough. Place the other half of the dough on a greased oven pan lined with baking paper (32 x 39 cm) and smooth it down with a pallet. Spread the dark dough over it. Using a fork, pull spirally into the light-coloured dough and smooth again. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for approx. 40 minutes. Remove and let cool off. Mix cream cheese, icing sugar, lemon juice and peppermint liqueur with the whisk of the hand mixer for about 5 minutes. Spread the cream evenly on the cooled down cake. Melt the couverture in a bowl on a warm water bath, fill into a freezer bag and cut off a small corner.
Remove and let cool off. Mix cream cheese, icing sugar, lemon juice and peppermint liqueur with the whisk of the hand mixer for about 5 minutes. Spread the cream evenly on the cooled down cake. Melt the couverture in a bowl on a warm water bath, fill into a freezer bag and cut off a small corner. Cut the cake into squares. Decorate cake pieces with the chocolate coating