Wash and stone the plums. Finely grind 75 g each of walnuts and hazelnuts. Beat the fat, 150 g sugar and vanilla sugar with the whisk of the hand mixer until foamy. Stir in eggs bit by bit. Add sour cream and mix. Mix flour and baking powder and stir into the fat egg mixture.
Fold the ground nuts into the dough. Put the dough on the greased fat pan of the oven, smooth it down, cover with the plums and bake in the preheated oven (electric oven: 175°C/ gas: level 2) for about 40 minutes. In the meantime, chop the remaining nuts. Caramelise the remaining sugar in a pan, deglaze with 125 ml water while stirring continuously, simmer for 4 minutes, add the nuts and simmer for another 2-3 minutes. Take the cake out of the oven, spread the caramelised nuts on top (leave a little to decorate), let it cool down and, if desired, sprinkle whipped cream dabs on top and sprinkle with brittle. Results in about 25 pieces