Preheat oven to 350○F. Spray a 9x13" baking pan lightly.

Combine butter, both sugars, vanilla, and eggs in electric mixer. Beat well. In a separate bowl mux cocoa, flour, baking soda and salt. Mix into batter. Mix in nuts if desired.

Poor into pregreased pan. Bake 35-45 minutes, till knife comes out clean.