In a bowl, blend the quark with the eggs, sugar, vanilla extract and pudding powder until you get a smooth, slightly runny mixture.
Pour the mixture into a buttered baking dish. Arrange the halved plums evenly on top and sprinkle with ground cinnamon. Bake at 175 °C for about 45 minutes, until the top turns golden.
Once out of the oven, let the cake cool completely, ideally at room temperature, so that the ingredients set and the cake is easier to slice.