Whisk together flour, xanthan gum, baking powder, and baking soda in a bowl. Set aside.
Cream together butter, sugars, and salt in a separate bowl.
Blend in the eggs & vanilla.
Blend in the dry ingredients.
Fold in the Reese’s candies.
Chill the dough for at least an hour.
Scoop the dough onto a baking sheet lined with parchment.
Bake for 10 minutes at 350F.