Wash the lemon, grate dry and peel the zest in zests. Cut the vanilla pod lengthwise and scrape out the pulp. Boil up the milk with half of the lemon zest and vanilla pulp, stir in the rice pudding. Cook over low heat stirring continuously for about 20 minutes. Fold in mascarpone and 75 g sugar to form a smooth mixture, set aside and allow to cool
Drain the sour cherries. Simmer with 100 g sugar and remaining lemon zests for about 10 minutes. Then fill into a high mixing bowl and puree with a chopping stick, let cool down
Melt the butter. Pour the cantuccini into a freezer bag, crush them with the dough roll and mix them with the butter. Spread the crumb mixture as a base in a square springform pan (24 x 24 cm) lined with baking paper and press down well
Spread the rice pudding evenly on the base and spread the cherry puree on top. Refrigerate for at least 4 hours (preferably overnight)
Finely chop the couverture with a knife and sprinkle over the cake just before serving
Waiting time approx. 5 hours