01 - Preheat oven to 350°F. Lightly grease a nonstick donut pan.
02 - In a large bowl, whisk together mashed bananas, milk, eggs, vegetable oil, granulated sugar, and vanilla extract until smooth.
03 - In a separate bowl, sift together all-purpose flour, baking powder, baking soda, ground cinnamon, and salt.
04 - Gently fold the dry mixture into the wet ingredients until just combined. Avoid overmixing to maintain a tender texture.
05 - Transfer batter to a piping bag or a resealable plastic bag with the corner snipped. Pipe the batter into the prepared donut pan, filling each cavity about three-quarters full.
06 - Bake for 12 to 15 minutes until donuts are golden and the tops spring back when lightly pressed.
07 - Remove from oven and let donuts cool in the pan for 5 minutes before transferring to a wire rack to cool completely.
08 - In a bowl, whisk powdered sugar, milk, and vanilla extract until smooth. Dip cooled donuts into the glaze, allowing excess to drip off. Let set for several minutes before serving.