Roughly chop the chocolate. Melt the butter and chocolate in a small saucepan over low heat while stirring. Pull aside and let cool down a bit. Roughly chop the walnuts, except for 12 pieces to garnish.
Beat eggs, sugar, except for 1 tablespoon for decoration, vanilla sugar and salt with the whisk of the hand mixer until thick and creamy. Add the chocolate-fat mixture while stirring. Mix the flour, baking powder and spices and stir into the dough with the chopped nuts. Place paper liners in the hollows of a muffin baking sheet. Spread the dough with 1 teaspoon in it.
Bake in a preheated oven (electric stove: 175 ° C, convection: 150 ° C) for about 25 minutes. Let cool on a wire rack.
Brush the remaining walnuts thinly with a little egg white, turn in the remaining sugar and allow to dry. Mix the icing sugar in the remaining egg white until smooth and brush the muffins with it. Press a sugared walnut into the moist icing and let it dry.