Preheat oven to 350° F. Spray a 6-cavity donut pan with nonstick cooking spray.
In a large mixing bowl, add the gluten free flour blend, sugar, baking powder, salt, and cinnamon and whisk to combine.
In a medium mixing bowl, whisk together the milk, butter, egg, and vanilla until completely combined.
Add the wet ingredients to the dry ingredients and stir together until just combined.
Transfer the batter to the prepared donut pan with a spoon, pastry bag, or large plastic storage bag. Snip the corner off the bottom of the storage bag and pipe the batter into the donut cavities.
Bake for 8 to 10 minutes or until the donut springs back when touched.
Allow the donuts to cool in the pan for 4 minutes before inverting onto a wire rack to cool.
Make the Cinnamon Sugar Topping:
In a small mixing bowl, stir together the sugar and cinnamon.
Brush the top of a donut with melted butter then dip in the cinnamon sugar mixture and place back on the wire rack. Repeat with each remaining donut.
Notes
Spray the donut pan with nonstick cooking spray to prevent any part of the donut from sticking. Even though the donut pans I use are non-stick, I still take the time to lightly grease them.
Use a piping bag to fill the cavities in the donut pan. The bag makes filling the donut wells a breeze. If you don’t have a piping bag you can spoon the batter into the pan or use a large plastic storage bag with the corner snipped off.
Allow the donuts to cool for a few minutes before inverting the pan onto a wire rack to finish cooling. The donuts are delicate when they come out of the oven and may break or crumble if removed from the pan too soon.
Brush the tops of the donuts with melted butter before dipping in the cinnamon-sugar mixture. The butter adds flavor and helps the sugar mixture stick to the donuts.