Wash, halve and stone the plums. Stir fat, sugar, vanillin sugar and salt for about 5 minutes until creamy. Stir in eggs one after the other, alternating with the custard powder. Mix flour and baking powder and finally stir in briefly together with the lemon juice. Spread the dough into a greased springform pan (26 cm Ø) dusted with flour.
Put plums on top. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for approx. 45 minutes. Sprinkle with sugar crystals and dust with icing sugar. Whipped cream tastes good with it