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.
PAN RECIPE: Prepare batter as above. Spread batter evenly in greased 15-1/2x10-1/2x1-inch jelly-roll pan. Bake at 375°F. for 20 to 22 minutes or until cookie begins to pull away from sides of pan. Cool completely in pan on wire rack. Cut into bars. About 48 bars.