Prep your pan: Heat your oven to 350°F (175°C). Line a 12-cup muffin tin with paper liners or lightly grease each cup.
Mash the bananas: In a large bowl, mash the bananas with a fork until mostly smooth with a few small lumps.
Whisk in wet ingredients: Add granulated sugar, brown sugar, oil, eggs, milk, and vanilla. Whisk until the mixture is well combined and glossy.
Combine dry ingredients: In a separate bowl, whisk flour, baking soda, baking powder, salt, and cinnamon until evenly blended.
Mix gently: Add the dry ingredients to the wet ingredients.
Use a spatula to fold until just combined. Stop when you no longer see streaks of flour. The batter should be thick and a bit lumpy.
Add mix-ins: Fold in chocolate chips, nuts, or both, if using.
Fill the cups: Divide the batter evenly among the muffin cups, filling each about 3/4 full.
Sprinkle a pinch of coarse sugar on top if you like a crunchy finish.
Bake: Place the pan on the center rack and bake 18–22 minutes, or until the tops are set and a toothpick inserted in the center comes out with just a few moist crumbs.
Cool: Let muffins cool in the pan for 5 minutes, then transfer to a wire rack to finish cooling. Enjoy warm or at room temperature.