1. Preheat oven to 350°.
2. Lightly spoon flour into dry measuring cups; level with a knife. Combine flour, baking soda, and salt.
3. Beat butter with a mixer at medium speed until fluffy. Add brown sugar, beating until blended. Add egg and vanilla, beating just until blended.
4. Gradually add flour mixture to butter mixture, stirring just until combined; fold in chocolate and walnuts. Drop by rounded teaspoonfuls 2 inches apart onto baking sheets coated with cooking spray.
5. Bake at 350° for 8 to 10 minutes or until lightly browned. Remove from pans, and cool completely on wire racks.