Preheat the Oven & Prep Pan
Preheat to 350°F (175°C).
Line a 12-cup muffin tin with paper liners or grease lightly.
Mash the Bananas
In a large mixing bowl, mash bananas until mostly smooth. A few small lumps are fine.
Mix Wet Ingredients
Stir in melted butter, brown sugar, granulated sugar, eggs, and vanilla until combined.
Whisk Dry Ingredients Separately
In another bowl, whisk flour, baking powder, baking soda, salt, and cinnamon.
Combine Wet & Dry
Gently fold dry ingredients into banana mixture until just combined. Do not overmix (a few streaks of flour are okay).
Add Nuts
Fold in chopped walnuts or pecans.
Scoop & Bake
Divide batter evenly into muffin cups (about ¾ full).
Sprinkle tops with extra nuts or sugar if desired.
Bake for 18–22 minutes, until a toothpick inserted in the center comes out clean.
Cool & Enjoy
Let muffins cool in the pan for 5 minutes, then transfer to a wire rack.
Serve warm or at room temperature.