Preheat your oven to 350°F (175°C). Lightly grease a donut pan with nonstick cooking spray. This simple step helps the donuts release easily after baking and keeps them from sticking to the pan.

In a large mixing bowl, whisk together the flour, baking powder, baking soda, cinnamon, and salt. Mixing these ingredients first helps distribute everything evenly throughout the batter for consistent flavor and texture.

In another bowl, mash the ripe bananas until mostly smooth. Add the brown sugar, egg, milk, melted butter, and vanilla extract. Stir well until all the ingredients are fully combined and smooth.

Pour the wet mixture into the bowl with the dry ingredients. Stir gently until just combined. Do not overmix the batter because that can make the donuts dense instead of soft and fluffy.

Spoon the batter into a piping bag or zip-top bag. Cut a small corner and pipe the batter into each donut cavity. Fill each one about three-quarters full for the best shape.

Place the pan in the oven and bake for 10 to 12 minutes. The donuts should look lightly golden and spring back when gently touched in the center.

Remove the pan from the oven and let the donuts cool for about five minutes. Carefully transfer them to a cooling rack and allow them to cool completely before glazing.

If making the glaze, whisk together powdered sugar, milk, and vanilla until smooth. Dip the cooled donuts into the glaze and place them back on the rack until the glaze sets.