In a small mixing bowl combine flour and baking powder.
Beat oil, sugar, and cocoa together in a large mixing bowl. Add eggs to oil and cocoa mixture one egg at a time, beating well after each addition. Stir in vanilla. Mix in flour mixture. Fold in nuts if desired. Chill the dough overnight.
Preheat oven to 350 degrees F (175 degrees C). Grease cookie sheet.
Roll dough into walnut-size balls and roll each ball in confectioners' sugar.