1. Heat oven to 375°F.
2. Stir together flour, cocoa, baking soda and salt. Beat butter, granulated sugar, brown sugar and vanilla in large bowl on medium speed of mixer until creamy. Add eggs; beat well. Gradually add flour mixture, beating well. Stir in chocolate chips. Add nuts, if desired. Drop by rounded teaspoons onto ungreased cookie sheet.
3. Bake 8 to 10 minutes or until set. Cool slightly; remove from cookie sheet to wire rack. Makes about 5 dozen cookies.