Wash plums, grate dry and cut in half. Remove stones and cut the halves in three. Cream 160 g sugar, vanilla sugar, salt and butter with the whisk of the hand mixer. Stir in 3 eggs one after the other. Mix 140 g flour, starch, sauce powder and baking powder. Stir the dough alternately with the milk in tablespoons. Immediately pour into a greased springform pan (26 cm Ø) sprinkled with breadcrumbs.
Spread 2/3 of the plums on the cake and bake in a preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for 40-50 minutes (stick test). After about 20 minutes, spread the remaining plums on the cake. In the meantime, whisk marzipan, 1 egg, 1 tablespoon sugar and 1 tablespoon flour with the whisk of the hand mixer until smooth. Pour the macaroon mixture into a piping bag with star-shaped spout. Take the cake out of the oven about 30 minutes before the end of the baking time, squirt the macaroon mixture onto the cake and bake until done. Take the cake out of the oven, remove from the edge and let it cool down on a cake rack. Dust with icing sugar before serving