01 - Set oven temperature to 350°F and lightly grease a nonstick donut pan to prevent sticking.
02 - In a large mixing bowl, whisk mashed bananas, milk, eggs, vegetable oil, granulated sugar, and vanilla extract until the mixture is fully 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 components until just combined, avoiding overmixing to maintain a tender crumb.
05 - Transfer the batter into a piping bag or resealable plastic bag with the corner snipped. Pipe the batter into each donut mold, filling each about three-quarters full.
06 - Place pan in preheated oven and bake for 12 to 15 minutes, or until donuts are golden and tops spring back when pressed lightly.
07 - Remove pan from oven. Allow donuts to rest in the pan for 5 minutes. Transfer to a wire rack to cool completely.
08 - In a medium bowl, whisk powdered sugar, milk, and vanilla extract until smooth. Dip cooled donuts into glaze and allow to set before serving.