1. Preheat the oven to 375°F (190°C). Lightly grease a 9 inches (23cm) tart tin (with slightly higher edges) or a springform tin and set aside. Wash, dry, halve and pit the plums for the topping. Cut those plum halves in half again lengthwise and set aside.

2. Mix flour, sugar, and ground cinnamon for the streusels in a bowl. Melt the butter, add to the bowl and mix everything until you have different sized streusels. Add the rolled oats and gently mix in. Place in the fridge until needed.

3. Mix the quark for the dough with the oil, egg, vanilla extract, and sugar in a large bowl. Combine the flour with baking powder, and salt and add to the bowl. Mix/knead to get a smooth dough. Roll out the dough on a floured surface slightly larger than the baking tin, transfer to the tin and press down on the bottom and sides.

4. Place the plums in circles on top of the dough, starting at the edge. Be sure to place the plums as close together as possible. Distribute the streusels evenly on top of the plums and sprinkle with some sliced almonds. Bake the plum cake in the preheated oven for about 28-30 minutes. Remove from the oven and let cool down completely. If you like, you can sprinkle the cake with some confectioners’ sugar before serving. Serve with whipped cream.