Preheat the oven to 350F. Line a muffin/cupcake pan with paper liners. Alternatively, spray the wells of the pan with baking spray.
In a medium bowl, whisk together the all purpose flour, baking soda and salt. Set aside.
2 cups all purpose flour, 1½ teaspoons baking soda, ½ teaspoon fine sea salt
Place the butter in a large bowl and cover with a paper towel. Microwave for 30-45 seconds until mostly melted.
½ cup unsalted butter
Whisk the granulated sugar into the melted butter.
¾ cup granulated sugar
Whisk in the eggs, one at a time.
2 large eggs, room temperature
Whisk in the vanilla, mashed banana and milk.
1 teaspoon pure vanilla extract, 1 cup overripe bananas, mashed, 2 tablespoons whole milk
Stir in the flour mixture, until just combined.
Divide the batter between the muffin liners, filling them about ¾ full.
Spoon a teaspoon of Nutella on the center of each muffin. Use a toothpick to swirl the Nutella throughout the muffins.
⅓ cup Nutella, or chocolate hazelnut spread
Bake the muffins for 20-22 minutes, until a toothpick inserted in the center comes out with a few moist crumbs.
Cool in the pan for 5 minutes before transferring to a cooling rack. Serve the muffins warm with extra Nutella.