For the short pastry, knead 250 g flour, 125 g butter, 75 g sugar, 1 packet vanilla sugar, lemon zest and egg with the dough hooks of the hand mixer to a smooth dough. Chill for about 30 minutes. Melt 125 g butter and let it cool down a little. Knead 175 g flour, 75 g sugar, salt and cinnamon with the butter to a crumbled dough. Wash, halve and stone the plums. Bring juice and 100 g sugar to the boil.
Steam the plums for about 5 minutes. Stir pudding powder and starch in a little water until smooth. Pour into the plums and bring to the boil again briefly. Set aside and let cool off. Roll out the short pastry on a floured work surface to a circle (30 cm Ø). Grease a springform pan (26 cm Ø). Put the dough in and press the rim. Prick the base several times with a fork. Spread plum compote on top. Sprinkle with crumbles. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for about 1 1/4 hours. Remove the cake and let it rest for a while.
Put the dough in and press the rim. Prick the base several times with a fork. Spread plum compote on top. Sprinkle with crumbles. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for about 1 1/4 hours. Remove the cake and let it rest for a while. Then remove the cake from the pan and let it cool down completely. Decorate with lemon balm as desired