Preheat the oven to 350°F (180°C) and line a 12-cup muffin tin with paper liners.

In a medium bowl, combine the flour, baking soda, cinnamon, and salt. Set aside.

In another large bowl, whisk the granulated sugar, brown sugar, melted butter, eggs, vanilla and bananas until thoroughly combined.

Fold the dry ingredients into the banana mixture until just combined. Take care not to overmix.

Divide batter evenly into prepared muffin cups and bake for 16-20 minutes, until a toothpick inserted into the center of the muffins come out clean.

Let the muffins cool in the pan for 10 minutes before transferring to a rack.

While the muffins are still warm, prepare the topping: combine the sugar and cinnamon in a bowl.

Brush the tops of the muffins with the melted butter, roll in the cinnamon-sugar and then return to the rack to let cool completely.

Store any leftover muffins in an airtight container at room temperature for up to two days. For longer storage, freeze for up to 2 months. Defrost at room temperature for about an hour or microwave briefly.