1. Heat oven to 350°F.
2. Stir together flour, cocoa, baking soda and salt. Beat butter, sugar, eggs and vanilla in large bowl until fluffy. Gradually add flour mixture, beating well. Stir in chocolate chips and nuts, if desired. Drop by rounded teaspoons onto ungreased cookie sheet.
3. Bake 8 to 10 minutes or just until set. Cool slightly; remove from cookie sheet to wire rack. Cool completely.