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