Completely line the cake pan (quiche pan) with baking release liner. Make the butter liquid in the frying pan.
Mix sugar with milk chocolate cubes, egg yolks, whipped cream and chocolate sprinkles. Add the hazelnuts, breadcrumbs and baking powder (1) to the mixture. Sprinkle everything together with rum.
Mix the relatively firm dough with the liquid butter until smooth. Whip the egg whites together with the salt and baking powder (2) until very stiff and stir into the prepared mixture. Then fill everything together into the prepared cake tin (quiche tin) and bake for about 45 to 50 minutes (test with a needle!) on the lowest shelf of the oven heated to 180 degrees. Rest the cake for about 10 min with the oven off and open. Once the cake has cooled completely, lift it out of the cake pan (quiche pan).
For the glaze, melt the dark chocolate together with the water in a water bath. Add the butter and let it melt as well. Add the powdered sugar and stir until smooth. Spread the glaze evenly over the cake using the back of a knife or a brush and dry at room temperature.
Wrapped in foil, this cake will keep in the refrigerator for a week without further ado. In general, it is a delicacy when enjoyed cooled.
Good luck!