Whisk together the GF flour, xanthum gum, baking soda, and salt in a bowl and set aside. Melt butter in a saucepan over medium heat. The butter will begin to foam. Whisk. After a couple of minutes, the butter will begin to brown on the bottom of the saucepan; continue to whisk and remove from heat as soon as the butter begins to brown and smells nutty. Immediately transfer the butter to a bowl to prevent burning. Set aside to cool for a few minutes.