Heat oven to 350 degrees.
In one bowl combine 1 cup + 1 Tbsp. Bob's Red Mil 1 to 1 flour, 1 tsp. baking powder, ¼ tsp. baking soda, ⅛ tsp. salt, 1 tsp. cinnamon, and ⅛ tsp. nutmeg. Stir ingredients until combined.
In another bowl add 1 large egg and mix. To the egg add ½ cup buttermilk, ½ packed cup brown sugar, and 1 tsp. vanilla extract. Stir until combined.
Add the dry ingredients to the wet a little at a time and stir until completely combined. The batter will be a little dense and sticky.
Spray a doughnut pan with cooking spray or grease with butter or oil to prevent sticking.
Place a heavy duty plastic bag in a mason jar or wide-mouthed glass. Pour the donut batter into the plastic bag. Remove the plastic bag, cut a hole in one of the bottom corners, and pipe the batter into the donut pan. You can also spoon the batter into the pan but I have found that piping it works well.
Place the pan in the oven and bake for 12 minutes.
Remove the pan and remove the donuts once they are cool enough to handle. Place them on a wire rack.
Melt 2 Tbsp. of butter in the microwave. Brush the entire surface of the donuts with the melted butter.
Mix ½ cup of sugar and 2 tsp. cinnamon in a small bowl.
Coat the donuts with the cinnamon/sugar mixture once they are brushed with the melted butter. The sugar mixture should stick to the surface of the donuts. Serve immediately.