Mix the butter with sugar, vanilla sugar and eggs until frothy. Stir in the flour with the baking powder.
Put the dough in a buttered pan and bake at 180 ° C for 30 minutes. Let cool down.
Mix the mascarpone with sugar, quark and lemon juice and spread it on the cake. Clean the strawberries in half and place on the cream.
Mix the icing with a little apple juice, bring the rest of the apple juice to the boil with sugar. Add the powder, bring it to the boil, let it cool down a little, and distribute it over the strawberries.