01 - Set oven to 350°F. Lightly grease a nonstick donut pan to prevent sticking.
02 - In a large bowl, whisk mashed bananas, milk, eggs, vegetable oil, granulated sugar, and vanilla extract until fully blended and smooth.
03 - In a separate bowl, sift together all-purpose flour, baking powder, baking soda, cinnamon, and salt.
04 - Carefully fold the dry mixture into the banana mixture, mixing just until ingredients are incorporated. Avoid overmixing to maintain a tender texture.
05 - Transfer batter to a piping bag or resealable plastic bag with a corner cut off. Pipe batter into the prepared donut pan, filling each mold approximately three-quarters full.
06 - Place pan in oven and bake for 12 to 15 minutes, or until donuts are golden and tops spring back when lightly touched.
07 - Remove pan from oven and let donuts cool in the pan for 5 minutes. Then transfer to a wire rack to cool completely.
08 - Whisk powdered sugar, milk, and vanilla extract until smooth. Dip fully cooled donuts into glaze, then set aside until glaze firms up.