Preheat your oven to 350ºF (175ºC) and grease a muffin tin for large or regular-sized muffins.

Mash 2 to 3 ripe bananas in a large mixing bowl. Stir in 1/4 cup melted butter, then add 2 eggs, 1/2 cup Greek yogurt, and 1 teaspoon vanilla extract, mixing until smooth.

In another bowl, whisk together 1 1/2 cups flour, 1 teaspoon baking soda, 1/2 teaspoon salt, and 1/2 cup sugar until well mixed.

Gently fold the dry ingredients into the wet mixture using a spatula until just combined. Some flour streaks are okay.

Fill muffin cups about 2/3 full with batter and drizzle 1/4 cup Nutella on top. Use a knife to swirl the Nutella into the batter.

Bake for 20-25 minutes for large muffins or 15-20 minutes for regular ones, until a toothpick comes out clean.

Let muffins cool in the tin for 15 minutes, then transfer them to a wire rack to cool completely.