Wash the mirabelles, drain, cut in half and remove the stones. Peel ginger and chop very finely. Mix the mirabelles and ginger. For the crumbles, chop the nuts coarsely. Put 75 g flour, 1 packet of vanilla sugar, 1 pinch of salt, 75 g sugar, 75 g butter and 1-2 tbsp water into a mixing bowl and work into crumbles with your hands.
For the batter, whisk 75 g butter, 1 pinch of salt, 1 packet of vanilla sugar and 75 g sugar until creamy. Stir in the egg. Mix 100 g flour and baking powder and stir in.
Put the dough into a greased springform pan (20 cm Ø) sprinkled with flour and smooth it down.
Spread the mirabelles evenly on top. Add the crumbles and bake in the preheated oven (electric range: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) for approx. 35 minutes on the middle shelf. Remove from the oven, place on a cake rack and allow to cool for about 1 hour.
Coarsely chop the chocolate coating and melt it over a warm water bath. Leave to cool a little. Remove the cake from the tin and place it on a cake plate. Pour the couverture into a piping bag, cut off the tip and decorate the cake with it in strips.
Allow the chocolate coating to dry and let the cake cool down completely.