Cut the chocolate into small cubes. Clean, wash and cut the rhubarb into pieces. Mix 1 tablespoon of flour into the rhubarb. Stir fat, sugar and salt for about 10 minutes until creamy. Stir in eggs one after the other.
Alternately stir in mineral water and approx. 6 tablespoons of flour. Mix remaining flour and baking powder and stir in briefly. Finally add rhubarb and chocolate to the dough. Grease a ring cake tin (23 cm Ø, approx. 2.5 litres capacity) and sprinkle with breadcrumbs. Fill in the dough and smooth it down. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for about 1 hour. Cool down on a cake rack. Turn the cake out of the tin and let it cool down completely. Mix icing sugar and cherry liqueur and coat the cake with it.
Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for about 1 hour. Cool down on a cake rack. Turn the cake out of the tin and let it cool down completely. Mix icing sugar and cherry liqueur and coat the cake with it. Leave to set for about 1 hour. Serve decorated with sugar crystals