01 - Preheat the oven to 350°F. Lightly grease a nonstick donut pan.
02 - In a large bowl, whisk together mashed bananas, milk, eggs, vegetable oil, granulated sugar, and vanilla extract until the mixture is smooth.
03 - In a separate bowl, sift together all-purpose flour, baking powder, baking soda, ground cinnamon, and salt.
04 - Gently fold the dry mixture into the wet ingredients until just combined. Avoid overmixing to maintain a tender crumb.
05 - Transfer the batter into a piping bag or a resealable plastic bag with a trimmed corner. Pipe the batter into the prepared donut pan, filling each cavity about three-quarters full.
06 - Bake for 12 to 15 minutes, or until the donuts are golden and the tops spring back when gently pressed.
07 - Remove from the oven and allow donuts to cool in the pan for 5 minutes. Carefully transfer to a wire rack and let cool completely.
08 - For the glaze, whisk together powdered sugar, milk, and vanilla extract until smooth. Dip cooled donuts into the glaze and allow to set before serving.