Mix the flour, baking powder and sugar together for the base. Add the softened butter and eggs, knead into a smooth dough and roll out or press onto a deep baking sheet (mine measures around 44 cm), forming an edge.
Mix together the oil, milk and starch for the poppy seed quark. Then stir in the eggs, quark, sour cream, sugar and poppy seeds and spread the mixture on the bottom. Wash the plums, dry them, cut them in half, remove the stones and spread them on the poppy seed quark. Preheat the oven to around 180 ° C.
For the crumble mix the flour, sugar and a pinch of salt. Melt the butter (do not fry or anything - just liquefy), mix in and spread as a crumble on the plums. Bake the cake for about 30-40 minutes, until the crumble and the edge / base brown lightly.
If you like, you can add some vanilla powder (ground vanilla pod) or grated lemon peel to the curd mixture.