Preheat and prep: Heat your oven to 375°F (190°C).
Lightly grease a mini muffin pan or line with mini paper liners.
Mash the bananas: In a large bowl, mash the bananas until mostly smooth. A few small lumps are fine.
Whisk the wet ingredients: Add the egg, milk, melted butter or oil, and vanilla. Whisk until combined.
Combine the dry ingredients: In a separate bowl, whisk flour, sugar (if using), baking powder, baking soda, salt, and cinnamon.
Bring it together: Add the dry ingredients to the wet.
Stir gently until just combined. Do not overmix—a few streaks of flour are okay.
Fold in extras: If using chocolate chips, blueberries, or nuts, gently fold them in now.
Fill the pan: Spoon batter into the mini muffin cups, filling each about 3/4 full. Top with a few oats or a tiny chocolate chip sprinkle if you like.
Bake: Bake for 10–12 minutes, or until the tops are set and a toothpick comes out clean or with a few moist crumbs.
Cool briefly: Let them rest in the pan for 3–4 minutes, then transfer to a wire rack to cool. This helps them set and keeps the bottoms from getting soggy.
Serve: Enjoy warm with a drizzle of honey or a swipe of peanut butter, or pack them for later.