01 - Preheat oven to 350°F. Lightly grease a 12-cavity donut pan with cooking spray or butter.
02 - In a large bowl, mash ripe bananas until completely smooth with no large lumps remaining.
03 - Whisk melted butter and brown sugar into mashed bananas until fully incorporated and mixture appears glossy.
04 - Add eggs, whole milk, and vanilla extract to banana mixture. Whisk vigorously until batter is uniform and smooth.
05 - In a separate medium bowl, whisk together flour, baking powder, baking soda, cinnamon, nutmeg, and salt until evenly distributed.
06 - Gradually fold dry ingredients into wet mixture using a spatula. Mix just until flour disappears—batter should remain slightly thick. Avoid overmixing to prevent tough donuts.
07 - Transfer batter to a piping bag or use a spoon to distribute evenly among donut pan cavities, filling each approximately 3/4 full.
08 - Bake for 10–12 minutes until tops are lightly golden and a toothpick inserted into the center comes out clean.
09 - Let donuts rest in pan for 5 minutes before carefully transferring to a wire rack. Cool completely before glazing.
10 - Whisk powdered sugar, milk, and vanilla in a small bowl until smooth and ribbon-like. Dip tops of cooled donuts into glaze and place back on rack to set.