In a medium bowl, sift together the oat flour, ground pepitas, xanthan gum, baking powder, and matcha powder. Set aside.
In the bowl of a stand mixer, beat the butter on medium high speed until light and fluffy. Gradually add the powdered sugar and beat on low until fully incorporated. Add the vanilla and beat to combine.
With the mixer on low speed, gradually add the dry ingredients to the butter and beat until fully combined. Scrape the sides and beat again for about 30 seconds.
Roll the dough between two sheets of parchment paper until it is about ⅛-inch thick. Set the flattened dough, with the parchment paper on a medium baking sheet and freeze it while you preheat the oven, or about 10 minutes.
Preheat the oven to 300°F.
Remove the dough from the freezer and peel off the top layer of parchment paper. Lift the parchment paper onto a cutting board and cut out the cookies using your favorite cookie cutter (anything between 1 and 2-inches will work!). Transfer the cutout cookies to a piece of parchment paper on the cold cookie sheet as you go.
Optional: sprinkle the cookies with sanding sugar (you can even press the cookies into the sanding sugar if you want!).
Bake cookies for 12-13 minutes, removing them earlier if you see the edges start to turn light brown (the color of your baking sheet may vary the cooking time).
Transfer the cookies with a spatula to a wire rack to cool and repeat until you've used up all the dough.
Notes
*I grind my own oat flour by pulsing gluten-free oats in the blender or food processor until fine, then sifting out any large pieces. **Raw unsalted pepitas are available on Amazon. I grind the pepitas/pumpkin seeds in the blender or food processor by pulsing, scraping the sides, and pulsing again until fine. Be careful not to run it too long or you'll end up building up heat and moisture. Sift out any large pieces and grind them again.
This nutritional information has been automatically calculated, and as such, may be incomplete or inaccurate. Please reference the specific ingredients you use for the most accurate nutritional information.