Wash the currants, drain well and pluck the berries from the stems, except for a few panicles for decoration. For the dough melt butter in a pot. Mix 500 g flour, 300 g sugar, baking powder, vanillin sugar and salt in a bowl.
Press a depression in the middle, add 1 egg and cover with flour from the rim. Add hot butter at once and knead with the dough hooks of the hand mixer. Sprinkle the rest of the flour (40-50 g) over the crumbled dough and mix in with your hands or by twirling.
Grease a round spring plate (approx. 32 cm Ø) and line it with parchment paper. Spread about 2/3 of the crumbly dough on the bottom and press it down to a firm base. Prick several times with a fork.
Pre-bake in the preheated oven, 2nd shelf from below (electric oven: 200 °C/ gas: level 3) for approx. 15 minutes. Meanwhile, grate marzipan coarsely for the icing and gradually mix with sour cream and remaining eggs to a smooth icing.
Finally, stir in the remaining sugar and bitter almond flavour. Pour the icing on the pre-baked base and spread the currants on top. Sprinkle with remaining crumbled dough and bake in the preheated oven, 2nd flush.
Bake from below (electric oven: 175 °C/ gas: level 2) for approx. 60 minutes. Let the cake cool down in the tin on a cake rack. Carefully remove the cake from the parchment paper with a knife and cut it into approx. 18 pieces.
Sprinkle with lemon balm leaves and remaining currants and decorate. Whipped cream tastes good with it.