01 - Preheat the oven to 350°F 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 smooth.
03 - In a separate bowl, sift together the all-purpose flour, baking powder, baking soda, ground cinnamon, and salt.
04 - Gently fold the dry ingredients into the banana mixture until just combined. Avoid overmixing to maintain a tender texture.
05 - Spoon the batter into a piping bag or a resealable plastic bag with the corner cut off, then pipe the batter into each donut mold, filling each about three-quarters full.
06 - Bake for 12 to 15 minutes, until golden brown and the tops spring back when lightly pressed.
07 - Remove from the oven; allow donuts to cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.
08 - For the glaze, whisk together powdered sugar, milk, and vanilla extract until smooth. Dip each cooled donut into the glaze and let set before serving.