Preheat oven to 400°F. In a large bowl, combine flour, sugar, baking powder, cinnamon, nutmeg and salt. Add mashed banana, egg, butter, milk and vanilla extract and stir until just combined. (Over-stirring will make donut tough)
Place batter in ziploc bag and squeeze out air. Cut corner of bag. Spray donut pan with non-stick spray. Pipe the batter evenly in the donut pan. It should make 6. Bake for 9-10 minutes or until stick comes clean. Remove from oven and remove from pan and cool on a cooling rack.
Brown Butter Glaze
Heat the butter in a small saucepan over medium heat, stirring often, until it foams and has a nutty aroma, about 5-7 minutes. Remove from heat.
Transfer the brown butter to a shallow bowl and add the sugar. Whisk to combine and then add in the vanilla extract to make a smooth, pourable glaze. Dip each donut in the glaze and place back on cooling rack. Allow glaze to set for 30 minutes before serving.
Notes
Even though they say non-stick, spray your donut pans with non-stick cooking spray to make sure the donuts come out.
Ripe bananas have a sweeter flavor and are easier to mash, making them ideal for the donuts
When measuring the flour, lightly spoon it into a measuring cup and then level it off with the back of a knife to get the right amount.
You can spoon the batter into the donut pans, but the easiest way to get the batter in the pan is by using a pastry bag or Ziploc bag with the corner cut off.
Just like with any cake type batter that you make, you’ll know the donuts are done when a toothpick comes out clean.
Let the baked donuts cool completely before you dip them in the glaze.