01 - Preheat oven to 350°F. Lightly grease a nonstick donut pan to prevent sticking.
02 - In a large mixing 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 ingredients into the banana mixture, mixing just until combined. Do not overmix to ensure a tender texture.
05 - Transfer batter to a piping bag or resealable plastic bag with a snipped corner. Pipe batter into prepared donut molds, filling each about three-quarters full.
06 - Bake in the preheated oven for 12 to 15 minutes, until donuts are golden and spring back when lightly pressed.
07 - Allow donuts to cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.
08 - In a small bowl, whisk powdered sugar, milk, and vanilla extract until smooth. Dip cooled donuts into the glaze and let set before serving.