Cream together the butter and powdered sugar until light and fluffy, then incorporate the egg.

Sift together the flour, black cocoa, Dutch process cocoa, and salt, then gradually mix into the wet ingredients.

Chill the dough for 30-45 minutes, then roll out to 1/4 inch thickness and cut into shapes.

Chill the cut shapes for about 1 hour, then bake at 160°C (320°F) for approximately 10 minutes.

Prepare royal icing with egg whites, powdered sugar, vanilla, and food coloring, then decorate the cooled cookies.

Allow the icing to dry for 3 to 6 hours before displaying or gifting.