Preheat the oven to 350 degrees. Line a muffin tin with paper liners and set aside.
In a large bowl or the bowl of a stand mixer, cream together the sugar and butter until light and fluffy.
Add the eggs, vanilla, milk, and mashed bananas, and mix until smooth.
Add the flour, salt, baking soda, and baking powder, and mix until just combined.
Scoop the batter into the prepared muffin tin, filling 3/4 full. Scoop a teaspoon of nutella onto the top of each muffin cup, then use a toothpick to swirl the nutella into the batter.
Bake 15-17 minutes, or until the muffins are golden brown on top, and a toothpick inserted into the center comes out clean.