Prepare a batter from the butter, milk, eggs, flour, sugar and cinnamon, which is at room temperature. At the end stir in the 3 teaspoons of baking powder and pour into a 28 mm springform pan. Smooth out the dough. Place the pitted plums in a circle on the dough (they sink into the dough when they are baked).
Heat the 3 tablespoons of butter with the 3 tablespoons of sugar and a pinch of cinnamon in a saucepan. Add the flour to the heated mass and stir with the kneading paddle until the crumble forms (add a little more flour if necessary). Pour the crumble over the dough and plum mixture.
Bake at 170 ° C (fan oven) for about 50-60 minutes in a hot oven.
The cake tastes very tasty with cream, under which a mug of sour cream has been placed.