1 Preheat oven to 350F
2 Put oat flour, powdered sugar, tapioca flour, baking soda, matcha powder, and salt in a food processor. Pulse to combine.
3 Whip egg whites until stiff with a whisk in a small metal bowl.
4 Add whipped egg whites, butter, and vanilla extract to the dry ingredients. Process until everything is combined and you have a soft, sticky dough. (Add 1T water if the mixture is too dry, or 1T oat flour if the mixture is too wet).
5 Spread the granulated sugar on a small plate.
6 Roll 1T of the dough into a ball, then roll in the sugar to coat.
7 Place the ball on a baking sheet lined with parchment paper and flatten slightly with your hand.
8 Repeat with remaining dough, spacing the balls 2 inches apart on the baking sheet. If the dough becomes too sticky, place in the fridge for 5 minutes to firm up.
9 Bake for approximately 8 minutes, until the tops have cracked, the edges have just started to firm, but the center is still soft..
10 Remove from oven, and cool on a wire rack for 10 minutes.
