In a large bowl, cream together butter and sugar. Beat in eggs and vanilla. Stir in flour, cocoa powder, baking powder and salt. Cover and refrigerate dough for at least one hour, or overnight.

Preheat oven to 400°F. Turn out dough onto surface dusted with cocoa powder. Roll dough out 1/4 inch thick. Cut into shapes with cookie cutter. Place cookies 1 inch apart on lightly greased baking sheets.

Bake 6 to 8 minutes in preheated oven. Cool completely. Frost and decorate if desired.