Preheat oven 375 F. Cream butter, sugars, vanilla, and cocoa powder. Stir in remaining ingredients and blend well. Refrigerate 30 mins. Drop dougn by rounded teaspoonsonto ungreased cookie sheet about 2" apart. Bake until cookies are set, 5-8 mins. Cool slightly and remove from pan. When making large cookies, press down slightly on cookie dough to help cook more evenly. Bake slightly longer, 8-10 mins.