Prepare the oven and pan Position a rack in the center of the oven and preheat it to 425°F (220°C). Line a standard 12-cup muffin pan with paper liners.

Combine the dry ingredients In a medium bowl, whisk together the flour, baking powder, baking soda, salt, and cinnamon. Continue whisking until the leavening and cinnamon are evenly distributed.

Mash the bananas Place the peeled bananas in a separate large bowl and mash them with a fork or potato masher. A few small soft lumps are fine, but there should be no large pieces.

Mix the wet ingredients Add the eggs, brown sugar, granulated sugar, melted butter, milk, and vanilla to the mashed bananas. Whisk until the mixture looks smooth and glossy, with no visible streaks of egg.

Finish the batter Add the dry ingredients to the banana mixture. Fold gently with a flexible spatula until only a few flour streaks remain. Add 3/4 cup (128 g) of the chocolate chips and continue folding just until evenly distributed. The batter should be thick and scoopable.

Fill the muffin cups Divide the batter evenly among the 12 lined cups, filling each about three-quarters full. Sprinkle the reserved 1/4 cup (42 g) chocolate chips over the tops.

Start at high heat Bake at 425°F (220°C) for 5 minutes. Without opening the oven door, reduce the temperature to 350°F (175°C).

Finish baking Continue baking for 13 to 16 minutes, for a total baking time of about 18 to 21 minutes. The muffins are done when the tops are rounded and golden, the centers spring back lightly, and a toothpick inserted away from a chocolate chip comes out clean or with a few moist crumbs.

Cool briefly in the pan Place the muffin pan on a wire rack and let the muffins cool for 5 minutes. The sides will firm slightly, making the muffins easier to remove without tearing.

Finish cooling Transfer the muffins from the pan directly to the wire rack. Cool for at least 15 minutes before serving so the crumb can finish setting.