Preheat oven to 375°F (190°C). Line a muffin tin with paper liners.
In a medium bowl, whisk together flour, baking soda, salt, and sugar.
In a large bowl, mash bananas until smooth. Add egg, melted butter, and vanilla, mixing well.
Add dry ingredients to the wet mixture and gently fold until almost combined.
Fold in chocolate chips until batter is just combined.
Divide batter evenly among muffin cups and top with extra chocolate chips if desired.
Bake the Banana Chocolate Chip Muffins for 17–20 minutes, or until a toothpick inserted in the center comes out clean.
Cool in the pan for 5 minutes, then transfer to a wire rack.