Wash and dry the plums. Cut them in half but make sure not to completely separate them, and remove the core.
Place a baking paper on a baking sheet and butter the paper lightly.
Preheat the oven at 210 degrees Celsius.
In a bowl mix the flour, baking powder, salt and pudding powder.
In a casserole melt the margarine and the sugar.
Add the eggs in the casserole and mix well.
While stirring add the flour mix in the casserole slowly. Continue to stir and add the milk until the batter is compact.
Pour the dough on the baking paper and press it out to the edges so it cover the bottom completely.
Put the plums evenly on top of the dough and sprinkle the vanilla sugar and the cinnamon on top.
Place the cake in the middle of the oven for 30 minutes.