Preheat the oven to 425℉/220℃ and line your muffin tins with 12 liners. Mash the bananas.
1 cup bananas
In a large bowl, whisk mashed bananas, oil, eggs, vanilla, sour cream, and dark brown sugar. Whisk until well combined. There may be lumps from the bananas but that is okay.
1 cup bananas, 1 1/4 cups dark brown sugar, 1/2 cup oil, 2 eggs, 3/4 cups full fat sour cream, 1 tbsp vanilla
Toss in flour, cinnamon, nutmeg, salt, cornstarch, baking powder, baking soda, and salt. Using a spatula, mix until just completely combined.
2 1/2 cups all-purpose flour, 2 tsps baking powder, 1/4 tsp salt, 1 tbsp cornstarch, 1 1/2 tsp cinnamon, 1/8 tsp nutmeg, 1 tsp baking soda
Evenly divide the batter between 16 liners, they should be almost or all the way full. Using a cookie scooper helps big time to minimize the mess. Sprinkle some white sugar on top.
1-2 tbsp white sugar for sprinkling
Bake the muffins at 425℉ for 5 minutes, then lower the oven to 375°F and bake for 15-18 minutes. The muffins are ready when they bounce back at touch or a toothpick inserted comes out clean.
These muffins stay fresh covered at room temperature for up to 3 days, and in an airtight container in the refrigerator for up to a week!