Cream fat, sugar and vanillin sugar. Stir in eggs one after the other, add milk. Mix flour and baking powder and stir in. Grease a springform pan (26 cm Ø) and sprinkle with breadcrumbs.
Pour in the dough and smooth it down. Bake in the preheated oven (electric oven: 175 °C/ gas: level 2) for approx. 20 minutes. Leave to cool in the tin on a cake rack. In the meantime, wash the plums, dab dry, quarter and stone them.
Bring 1/8 litre of plum nectar, 70 g sugar, cinnamon stick, 2 tablespoons lemon juice, lemon peel and plums to the boil in a pot. Cover and stew for 4-5 minutes. Take some slices of plums out of the pot for decoration and let them drip off.
Stir starch and remaining juice until smooth. Stir into the compote and bring to the boil again briefly. Remove cinnamon stick and lemon peel and spread the compote on the sponge base. Let it cool down.
Mix mascarpone, quark, remaining sugar, vanillin sugar, remaining lemon juice and grated lemon peel. Whip the cream and cream firmer until stiff. Fold into the mascarpone cream and spread on the plum compote.
Spread a few drops of plum jam on the cream and wave it through the cream with a spoon. Put the cake in a cool place for about 1 hour. Remove from the tin and decorate with plum wedges. Serve dusted with cinnamon.