Preheat oven to 350°F. Grease a large cookie sheet or line with parchment paper; set aside.
Stir together the GF baking flour, baking soda, xanthan gum and salt; set aside.
In a large mixer bowl, beat butter (room temperature, not melted) with granulated sugar, brown sugar, vanilla and egg; scrape sides of bowl frequently. Beat in flour mixture on low speed, mixing thoroughly. Stir in chocolate chips and nuts.
Shape dough into flat disk, wrap tightly with plastic wrap and chill for 2 hours. Drop by tablespoonfuls 2” apart on baking sheet, or roll into balls if dough is hard to work with. Bake 10-12 minutes on center rack of oven or until lightly browned. Cool 2-3 minutes before removing from cookie sheet.
