Add and combine white rice flour, tapioca flour, brown rice flour, xanthan gum, baking soda, baking powder, ground cinnamon, and salt to a bowl. Set the dry ingredients aside.

Using a standalone mixer, with the paddle attachment fitted or handheld mixer, beat the butter, brown sugar, and white granulated sugar on medium-high speed until light and fluffy (2-3 minutes). Then, add the eggs one at a time and beat until combined. Pour the vanilla extract and mix until combined. Now, add the dry ingredient and beat at low speed until combined.

Wrap the dough with plastic wrap and chill it for 30 minutes.

Preheat the oven to 180°C (356°F)

Roll three tablespoons of oatmeal cookie dough into a ball, and transfer it to a baking tray aligned with parchment paper at least 5 cm ( 2 inches ) apart.

Bake the cookies for 10-12 minutes or until the edges are golden. Allow the cookies to cool down on the tray for 5 minutes before transferring them to a cooling rack.