In a large bowl of a hand-held or stand mixer with a paddle attachment, mix the butter on medium speed for 1 minute until smooth. Add the brown sugar and mix for about 3 minutes, scraping down the bowl every minute until incorporated, light and fluffy. Add the egg and mix for 30 seconds, scraping down the bowl. Add the vanilla and mix for 30 seconds.

In a separate medium sizes bowl, whisk the oat flour, xantham gum, baking soda and salt together until combined and there are no lumps. Add the dry mixture one cup at a time to the wet mixture and mix on low speed until incorporated. Turn off the machine and fold in the white chocolate chips, cranberries and the pistachios with a spatula.

Cover the dough with plastic wrap and chill for 2-4 hours in the fridge.

Preheat oven to 350 degrees Fahrenheit. Remove the dough from the fridge..

Line two large baking sheets with silicone baking mats, or parchment paper.* Using a tablespoon scoop (spray it with cooking oil so it doesn't stick) Scoop the dough into balls, rolled between your hands (also sprayed) and continue until you've done all of the balls. Leave a bit of space in between each cookies, about 3 inches. Ensure the cookies are still cold when going into the oven so they get high and fluffy and not thin and flat.

Bake for 11-13 minutes until the cookies are slightly golden brown. Remove from oven and allow cookies to cool for 5 minutes before removing from sheet (they will be very soft straight out of the oven but firm up when cooled a bit).