Preheat oven (electric cooker: 175 °C/circulating air: 150 °C/gas: see manufacturer). Melt butter, let cool down a little. Mix 600 g flour, baking powder, 1 pinch of salt, sugar, lemon peel, eggs and liquid butter with the dough hooks of the mixer to form crumbles.
Approx. 1⁄3 Cover the crumble and leave to cool for approx. 30 minutes.
Spread the remaining crumbles on a greased baking tray (approx. 35 x 40 cm). Press down with your hands to form a flat base. Spread plum puree evenly on top. Mix the remaining crumbles and 2-3 tbsp. flour briefly and sprinkle over the plum puree.
Bake in a hot oven on the lowest shelf for about 20 minutes.
Bake on the middle shelf for about 15 minutes until done. Let the tartlets cool down and cut into pieces. Serve with semi-stiff whipped cream and a little cinnamon.