Preheat the oven to 350°F (175°C) and line a muffin tin with paper liners.

In a mixing bowl, whisk together the flour, baking soda, and salt.

In another bowl, combine the mashed bananas, granulated sugar, brown sugar, melted butter, eggs, and vanilla extract until smooth.

Gradually add the dry ingredients to the wet ingredients, stirring until just combined.

Spoon the batter into the prepared muffin tin, filling each cup about 2/3 full.

Drop a spoonful of Nutella on top of each muffin and use a toothpick to swirl it into the batter.

Bake in the preheated oven for 18-20 minutes, or until a toothpick inserted into the center comes out clean.

Allow the muffins to cool in the tin for 5 minutes before transferring to a wire rack to cool completely.