Preheat oven to 350° F and line an 8x8 in baking pan with foil or parchment paper, leaving an overhang on all sides to easily remove once baked.
In a medium bowl, whisk the gluten free flour, baking powder, baking soda, salt and 1 teaspoon cinnamon together and set aside.
In a large bowl, whisk together the melted butter, brown sugar and granulated sugar. Add the egg and vanilla, whisking until combined. Slowly add the flour mixture into the wet ingredients, mixing with a large wooden spoon or rubber spatula being careful not to overmix.
Spoon half the batter into the prepared pan and spread evenly to the corners. Evenly sprinkle half of the cinnamon sugar mixture over the top of the batter. Spoon the rest of the batter over and spread evenly to the corners. Sprinkle the rest of the cinnamon sugar over the top of the batter. Bake for 25 minutes or until light golden brown on top and a toothpick inserted in the center comes out clean.
Allow to cool completely in the pan on wire rack. Once cool, lift the foil or parchment paper out of the pan using the overhang on the sides and cut into squares. Keep in an air tight container at room temperature for 5 days or in the freezer for up to 2 months.