Combine sugar, flour, cocoa, baking powder, salt, and black walnuts; set aside. Combine oil, eggs, and vanilla; add to dry ingredients. Do not over mix. Spread in a 13x9x2-inch baking pan. Bake in preheated 350° oven for 20 to 25 minutes or until toothpick inserted in center comes out clean. Makes 2 dozen.