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 smooth.
03 - In a separate bowl, sift together all-purpose flour, baking powder, baking soda, cinnamon, and salt.
04 - Fold the dry ingredients into the wet mixture just until incorporated. Avoid overmixing for a tender crumb.
05 - Transfer batter to a piping bag or a resealable plastic bag with a snipped corner. Pipe batter into the prepared donut pan, filling each well three-quarters full.
06 - Bake in the preheated oven for 12 to 15 minutes, or until donuts are golden and tops spring back when lightly pressed.
07 - Let donuts cool in the pan for 5 minutes before transferring to a wire rack to cool completely.
08 - For the glaze, whisk powdered sugar, milk, and vanilla extract until smooth. Dip cooled donuts into the glaze and allow to set before serving.