Preheat the oven to 350°F (175°C) and grease a donut pan.

In a mixing bowl, mash the ripe bananas until smooth.

Add eggs, sugar, milk, and melted butter to the mashed bananas; mix well.

In another bowl, combine flour, baking powder, and cinnamon. Gradually add to the wet mixture until just combined.

Spoon the batter into the donut pan, filling each cavity about three-quarters full.

Bake for 10-12 minutes or until golden brown and a toothpick comes out clean. Let cool slightly before transferring to a wire rack.