Put the quark, flour, sugar, vanilla sugar, baking powder, oil and milk in a bowl and knead into a smooth dough.
Wash the plums and cut in half.
Molding:
Mix the sour cream, eggs, sugar and custard powder with the whisk.
Preheat the oven to 180 ° C fan oven.
Grease a round baking pan (approx. 28 cm) well. Roll out the dough on a lightly floured work surface and place in the baking pan, pulling up the edge approx. 2 - 3 cm. Spread the plums on top and pour the icing over it.
Bake the cake for about 15 minutes WITHOUT the crumble.
Streusel:
Knead the flour, butter, almonds, sugar, salt, cinnamon and vanilla sugar with your fingers. If the dough is still too sticky, just add a little flour. If you like, you can mix in almond sticks.
After 15 minutes of baking, take the cake out of the oven, spread the crumble on top and bake the cake for another 20-30 minutes.