Preheat oven 350 F.In a large mixing bowl, beat the butter until creamy. Gradually add both sugars, then gradually add the eggs. Beat until light and fluffy, then beat in the cocoa powder.
Combine the flour, baking soda and salt in a separate bowl and stir well, then stir into the batter.
Add the chocolate chunks or chips and white chips (if using). Chill the dough for at least 30 minutes.Drop dough by rounded teaspoons or tablespoons onto ungreased or foil lined baking sheets spacing about 2 1/2 inches apart.
Bake until cookies are set, 8-10 minutes for small cookies or up to 12 minutes for larger cookies.
Let the cookies cool in the baking sheet for about 5 minutes, then transfer to a wire rack and let cool completely.
