Beat butter with sugar, then add eggs and spin for a few minutes.
Remove the whisk from the kneading machine and attach the flat beater, then incorporate the flour previously sifted with cocoa, baking powder and vanillin. Spin at low speed until the dough is amalgamated, then remove it from the mixer.
Form well distributed biscuits on the trays and decorate them with grains of sugar, hazelnuts, chocolate sprinkles or other pastry decorations.
Preheat the oven and cook following the parameters (see pdf).