Step 1

Preheat oven to 350 degrees F (175 degrees C). Grease a muffin tin.

Step 2

Sift flour, baking powder, baking soda, cinnamon, salt, and nutmeg together in a small bowl.

Step 3

Mash bananas in a large bowl. Mix in white sugar, melted butter, brown sugar, egg, and vanilla extract. Fold in flour mixture until just combined. Fold walnuts into the batter.

Step 4

Divide batter evenly among the muffin cups.

Step 5

Bake in the preheated oven until a toothpick inserted into the center comes out clean, about 20 minutes.