Mash the bananas until mostly smooth with some small chunks remaining—this texture adds nice dimension to the muffins. Measure out all dry ingredients (flour, sugar, baking soda, baking powder, cinnamon, nutmeg, and salt) and whisk them together in a medium bowl to distribute the leavening agents evenly. Prepare the streusel topping by combining the 3/4 cup flour, brown sugar, cinnamon, and salt in a separate small bowl. Cut the cold butter into 1/2-inch cubes and add to the streusel mixture, then use a fork or your fingertips to work it into coarse crumbs—this creates the crumbly texture we want for the topping. Preheat your oven to 425°F.

In a large bowl, combine the mashed bananas, vegetable oil, room-temperature eggs, and vanilla. Whisk vigorously for about 1 minute until the mixture is well combined and slightly emulsified—this helps create a tender crumb. The eggs should be at room temperature because they incorporate more smoothly and create a better texture than cold eggs.

Pour the dry ingredient mixture from Step 1 into the wet mixture from Step 2. Using a wooden spoon or spatula, fold everything together with as few strokes as possible—just until the flour streaks disappear. Overmixing develops gluten and creates tough, dense muffins, so resist the urge to stir vigorously. Fold in the chocolate chips until evenly distributed, then let the batter rest for 15 minutes. This resting period allows the flour to fully hydrate and helps the muffins bake more evenly.

Place paper liners in every other hole of a standard 12-cup muffin pan—this prevents the muffins from touching and allows them to bake more evenly with better browning on the sides. Divide the rested batter evenly among the lined cups, filling each about three-quarters full. Generously top each muffin with a spoonful of the streusel mixture from Step 1, then sprinkle a few extra chocolate chips on top for added richness and visual appeal.

Bake at 425°F for 7 minutes to set the tops and create a golden crust, which locks in moisture. Then lower the oven temperature to 350°F and bake for 16-18 minutes longer, until a toothpick inserted into the center comes out with just a few moist crumbs. The high-heat blast at the start creates lift and browning, while the lower temperature finishes the bake gently so the insides stay moist and tender. Let the muffins cool in the pan for 5 minutes before removing—I find this helps them hold together while still being easy to extract from the liners.

Transfer the muffins to a wire cooling rack and let them cool for at least 20 minutes before serving. The muffins will continue to set as they cool and develop better flavor at room temperature. If you only have one muffin pan, repeat Steps 4-5 with the remaining batter for a second batch of muffins. These muffins are best eaten the same day but will keep in an airtight container for 2-3 days.