01 - Preheat oven to 350°F. Lightly grease a nonstick donut pan to ensure easy donut removal.
02 - In a large mixing bowl, whisk together the mashed bananas, milk, eggs, vegetable oil, granulated sugar, and vanilla extract until the mixture is fully blended and smooth.
03 - In a separate bowl, sift together all-purpose flour, baking powder, baking soda, ground cinnamon, and salt to evenly distribute the leavening agents and spices.
04 - Gently fold the dry mixture into the banana mixture using a spatula until just combined. Avoid overmixing to preserve a tender donut structure.
05 - Transfer batter to a piping bag or a resealable plastic bag with the corner trimmed. Pipe the batter into each donut mold, filling each cavity approximately three-quarters full.
06 - Bake in the preheated oven for 12 to 15 minutes, or until the donuts are golden and their tops spring back when gently pressed.
07 - Remove the pan from the oven and let the donuts cool in the pan for five minutes before transferring them to a wire rack to cool completely.
08 - Whisk powdered sugar, milk, and vanilla extract together in a small bowl until smooth. Dip cooled donuts into the glaze and set on a rack until the glaze is set.