01 - Preheat oven to 350°F (175°C) and lightly grease a nonstick donut pan.
02 - In a large mixing bowl, whisk together the mashed bananas, milk, eggs, vegetable oil, granulated sugar, and vanilla extract until well blended.
03 - In a separate bowl, sift together the all-purpose flour, baking powder, baking soda, ground cinnamon, and salt.
04 - Gently fold the dry mixture into the wet ingredients until just combined, taking care not to overmix.
05 - Transfer the batter to a piping bag or a resealable plastic bag with a snipped corner and pipe batter into the prepared donut pan, filling each mold about three-quarters full.
06 - Bake for 12 to 15 minutes or until donuts are golden and tops spring back when gently pressed.
07 - Remove from oven and allow donuts to cool in the pan for 5 minutes before transferring to a wire rack to cool completely.
08 - Whisk powdered sugar, 2 to 3 tablespoons milk, and vanilla extract until a smooth glaze forms.
09 - Dip cooled donuts into glaze and allow glaze to set briefly before serving.