Grease a fat pan (deep baking tray; approx. 32 x 39 cm) and dust with flour. Finely grate the chocolate. Separate ##eggs##.
Preheat oven (electric cooker: 200°C/circulating air: 175°C/gas: level 3). Cream butter, sugar and 1 pinch of salt with the whisks of the mixer. Stir in egg yolk. Mix ##nuts## and baking powder.
Stir in chocolate and liqueur briefly. Beat the egg whites in a large bowl until stiff in portions and also fold in portions.
Spread the dough on the fat pan. Bake in the hot oven for about 20 minutes. Remove and let cool on a cake rack.
##Whisk the sour cream briefly with the whisk of the mixer, allowing the vanilla sugar to trickle in. Spread loosely on the cake.
Peel the mangos, cut the flesh off the stone and dice finely. Spread on the sour cream. Cut the cake into pieces.