Simmer 125 g butter, 100 g sugar and cream for about 4 minutes. Grate the marzipan. Stir almond flakes and marzipan into the butter mixture. Stir 250 g butter, 250 g sugar and vanilla sugar until creamy.
Stir in the eggs one by one. Mix flour and baking powder. Alternate with the milk and stir in briefly. Spread on a greased deep baking tray. Press small hollows into the dough with a teaspoon.
Spread plum jam in it. Spread the butter mixture evenly over it. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for approx. 25 minutes. While still hot, sprinkle with 4 tablespoons of sugar and allow to cool.