Beat eggs and sugar until fluffy, then add salt and butter and mix until homogeneous. Stir in flour, cocoa powder and baking powder and pour into a cake tin measuring 18 cm in diameter. Bake for 45 minutes in a pre-heated convection oven at 160°C. Then leave to cool for approx. 2 hours.
Slice the sponge into four layers and set aside.
Melt each of the types of chocolate. In the meantime, mix the quark with sugar and beat the cream until stiff. Fold the cream into the quark and divide the mixture into roughly 3, 250 g portions. Mix each of the melted types of chocolate into one portion of the quark mixture.
Spread the white chocolate mixture on the bottom layer of the cake, then place the next layer on top. Spread the milk chocolate mixture on this layer, then place the third layer on top. Spread the plain chocolate mixture on this layer and then place the last layer on top.
Caramelise the sugar in a pan. Then add butter, salt and cream and gently simmer until the lumps of sugar have melted. Pour the warm caramel onto the cake and place it in the fridge for at least 3 hours.