01 - Set oven to 350°F. Lightly grease a nonstick donut pan to ensure easy release.
02 - Combine mashed bananas, milk, eggs, vegetable oil, granulated sugar, and vanilla extract in a large mixing bowl. Whisk until fully incorporated and smooth.
03 - In a separate bowl, sift together all-purpose flour, baking powder, baking soda, ground cinnamon, and salt to evenly distribute leavening agents and spices.
04 - Gently fold the sifted dry ingredients into the wet mixture just until no dry spots remain; avoid overmixing to ensure a tender crumb.
05 - Transfer batter to a piping bag or resealable plastic bag with the corner snipped off. Pipe batter into prepared donut pan cavities, filling each about three-quarters full.
06 - Bake in the preheated oven for 12 to 15 minutes, until donuts rise, turn golden, and tops spring back when gently pressed.
07 - Remove from oven and allow donuts to rest in the pan for 5 minutes. Transfer to a wire rack to cool completely.
08 - In a bowl, whisk powdered sugar, 2 tablespoons milk, and vanilla extract until smooth. Adjust milk for desired consistency. Dip cooled donuts in glaze and set on the rack until glaze is set.