For the chocolate nut cake with chestnut flour, first separate the eggs. Beat egg whites briefly, then add granulated sugar and beat until stiff.
Beat egg yolks with powdered sugar until foamy. Add 1 shot rum, cooking chocolate and grated nuts. Gently mix in the chestnut flour (may be a bit lumpy) and stir in a shot of mineral water.
Fold in the beaten egg whites and pour into a greased and floured loaf pan. Bake the chocolate nut cake with chestnut flour at medium heat on the lowest setting.