01 - Preheat the oven to 350°F. Lightly grease a nonstick donut pan with oil or nonstick spray.
02 - In a large mixing bowl, thoroughly whisk together the mashed bananas, milk, eggs, vegetable oil, granulated sugar, and vanilla extract until the mixture is smooth and fully blended.
03 - In a separate bowl, sift together the all-purpose flour, baking powder, baking soda, ground cinnamon, and salt to ensure even distribution.
04 - Gently fold the dry ingredients into the wet mixture, mixing until just combined. Avoid overmixing to maintain a tender crumb.
05 - Transfer the batter into a piping bag or a resealable plastic bag with one corner snipped. Pipe the batter into the prepared donut pan, filling each mold about three-quarters full.
06 - Place the pan in the oven and bake for 12 to 15 minutes, or until the donuts are golden and the tops spring back when lightly pressed.
07 - Remove the baked donuts from the oven. Allow them to rest in the pan for 5 minutes, then transfer to a wire rack to cool completely.
08 - To make the glaze, whisk powdered sugar, milk, and vanilla extract in a bowl until perfectly smooth. Dip cooled donuts into the glaze and set them aside for a few minutes until the glaze sets.