01 - Preheat the oven to 350°F. Lightly grease a 12-cavity donut pan with cooking spray or butter.
02 - In a large bowl, mash the bananas until smooth. Whisk in the melted butter and brown sugar until well combined and slightly thickened.
03 - Add the eggs, milk, and vanilla extract to the banana mixture. Whisk until completely smooth and uniform in color.
04 - In a separate medium bowl, whisk together the flour, baking powder, baking soda, cinnamon, nutmeg, and salt until evenly distributed.
05 - Gradually fold the dry ingredients into the wet ingredients using a spatula. Mix until just combined—some small lumps are acceptable. Do not overmix as this can make donuts tough.
06 - Spoon or pipe the batter into the prepared donut pan, filling each cavity about 3/4 full. Use a spoon or small offset spatula to smooth the tops if needed.
07 - Bake for 10–12 minutes, or until the tops are lightly golden and a toothpick inserted into the center comes out clean. Rotate the pan halfway through for even baking.
08 - Remove from the oven and let the donuts cool in the pan for 5 minutes. Carefully transfer them to a wire rack to cool completely before glazing.
09 - In a small bowl, whisk together powdered sugar, 1 tablespoon of milk, and vanilla until smooth. Add more milk 1 teaspoon at a time until desired consistency is reached. Drizzle over cooled donuts or dip the tops into the glaze.