Beat the butter with the sugar until frothy. Gradually add the eggs while beating and mix the flour, baking powder and salt in a bowl and stir it evenly into the fat and egg mixture.
Finally stir in the ground hazelnuts and the uneven chocolate pieces and fill the dough into a greased and floured loaf pan.
Bake the cake for 45-50 minutes and then definitely do the stick test. Maybe and depending on the oven, you should cover the cake for the last 15 minutes so that it does not get too dark.
Take the nut cake out of the oven and let it cool down a little in the tin, then cool completely on a wire rack.
Mix the icing sugar and water into a thick icing and use it to coat the cake thickly.