Heat the oven to 175°C / 350°F. Grease a 24-cup mini muffin pan very well, including the top surface around the wells, using baking spray with flour or butter plus a light dusting of flour if needed. These bites are small and get coated later, so clean release matters here more than in a standard muffin recipe — an under-greased pan lets the edges stick and tear when it's time to unmold.

Whisk together the flour, baking powder, baking soda, salt, cinnamon, and nutmeg in a medium bowl until evenly combined, making sure the leavening and spices are distributed throughout.

Mash the bananas in a large bowl until mostly smooth, with a few tiny soft lumps fine but no large chunks remaining. Add the brown sugar, granulated sugar, melted butter, egg, sour cream or Greek yogurt, and vanilla, then whisk until smooth and fully combined. The mixture should look glossy, creamy, and loose enough to whisk easily, with the bananas fully incorporated so the batter bakes evenly.

Add the dry ingredients to the wet mixture and fold gently with a spatula just until no dry flour remains — the batter should end up thick but scoopable. Don't overmix, since that makes the bites tougher and less tender; stop as soon as the batter looks uniform. If your bananas were small and the batter seems overly stiff, add 1 to 2 teaspoons of milk; if they were extra large and the batter seems very loose, let it sit 2 to 3 minutes so the flour hydrates before adjusting further.

Divide the batter evenly among the 24 mini muffin cups, filling each about ¾ full, using a small cookie scoop or piping bag for a cleaner fill. Don't overfill — overfilled cups mushroom too much during baking and lose their neat bite-sized shape.

Bake for 12 to 14 minutes, until the tops are lightly golden, the centers spring back when touched, and a toothpick inserted in the center comes out clean or with a few moist crumbs. Don't overbake — these should come out baked through but still soft, so pull them as soon as the centers are set, since extra time in the oven dries out the banana crumb quickly.

Let the bites cool in the pan for 5 minutes only, then loosen gently if needed and transfer them to a rack or tray. Remove them while they're still warm — left too long in the pan, trapped steam softens the outer crust and makes them stick more rather than less.

While the bites are baking or cooling, mix the granulated sugar and cinnamon together in a shallow bowl, and place the melted butter in a separate bowl ready for dipping.

While the bites are still warm, dip or brush each one lightly with melted butter, then roll immediately in the cinnamon sugar until fully coated, working in small batches. Coat them while warm, not hot and not fully cold — warm bites let the butter cling without turning greasy, and the sugar adheres best at exactly this stage. Brush rather than dip for a lighter finish, or dip fully and roll generously for a heavier, more donut-style coating.