01 - Preheat oven to 350°F. Lightly grease a 12-cavity donut pan with cooking spray or butter.
02 - Mash bananas in a large bowl until smooth. Whisk in melted butter and brown sugar until combined. Add eggs, milk, and vanilla, whisking until smooth.
03 - In a separate bowl, whisk together flour, baking powder, baking soda, cinnamon, nutmeg, and salt until well blended.
04 - Gradually fold dry ingredients into wet mixture until just combined. Avoid overmixing to keep donuts tender.
05 - Spoon or pipe batter evenly into prepared donut cavities, filling each about 3/4 full.
06 - Bake for 10-12 minutes until a toothpick inserted into a donut comes out clean.
07 - Let donuts cool in pan for 5 minutes, then transfer to wire rack to cool completely.
08 - Whisk powdered sugar, milk, and vanilla in small bowl until smooth. Drizzle or dip cooled donuts in glaze.