Whisk all ingredients well except for the plum jam. Pour into a square, greased 25 cm form. Spread some plum jam over the whole cake in small blobs. This works best with 2 teaspoons.
Bake at 190 ° C for about 30-40 minutes. Let cool and cut into squares. Dust with icing sugar if you like.
If you don`t like it so sweet, you can slightly reduce the amount of sugar, we like the slices just that.
A 28 springform pan also fits, then it turns out to be a round cake.
In a 26 cm springform pan, the cake is only slightly higher and the baking time may need to be slightly longer depending on the oven.