Mix flour, 200 g sugar, lemon zest, baking powder and salt. Add egg yolk and fat and knead into crumbles. Put 2/3 of the crumbles into a greased tart tin with a removable bottom (26 cm Ø) and press to a smooth base. Chill for about 30 minutes. Wash and stone the plums and spread them on the base. Spread the rest of the crumbles on top and sprinkle with 50 g sugar.
Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) on the lower rack for approx. 25 minutes. Bake on the middle rack for another 25 minutes. Remove from oven and let cool for about 10 minutes. Remove from the tin and allow to cool. Serve decorated with mint and a dash of cream