1In small bowl, mix flours, the cream of tartar, baking soda, baking powder, xanthan gum and salt; set aside.
2In medium bowl, beat remaining ingredients except coarse sugar with electric mixer on low speed 1 minute or until well blended. Add flour mixture; beat until blended. Shape dough into a ball. Wrap in plastic wrap; refrigerate at least 2 hours.
3Heat oven to 350°F. Spray cookie sheet and rolling pin with cooking spray (without flour). On nonstick baking mat or cooking parchment paper sprayed with cooking spray (without flour), roll dough to 1/4-inch thickness. Using 3- to 3 1/2-inch cookie cutter, cut shapes from dough; place 1 to 1 1/2 inches apart on cookie sheet. Sprinkle with coarse sugar.
4Bake 10 to 15 minutes or until set and edges are lightly browned. Immediately remove from cookie sheet to cooling rack.