Step 1Heat the oven to 300 degrees. Lightly grease cookie sheets or line them with parchment.
Step 2In the bowl of a stand mixer using the paddle attachment, or in a large bowl using an electric mixer, cream together the butter and powdered sugar until well-blended. Beat in the vanilla and nuts to combine.
Step 3In a medium bowl, whisk together the flour, xantham gum and salt. Add this to the butter mixture and beat just until incorporated and a dough is formed.
Step 4Scoop about 1 teaspoon of dough and roll into a small ball. Place the dough on a prepared cookie sheet, and repeat with the remaining dough, spacing the cookies about 1 to 1 1/2 inches apart.
Step 5Bake the cookies until set and a light golden-brown on the bottom, 30 to 35 minutes. Set the cookies aside to rest for 5 minutes, then roll in powdered sugar to coat completely. Once they are cooled, roll the cookies again in sugar to cover.
Step 6The cookies are best made one day in advance.