Preheat the oven to 350°F. Butter and flour a loaf pan, using a parchment sling, if desired (see Notes).
4 tablespoon unsalted butter, softened
Sift the flour, baking powder, salt, and baking soda into a small bowl.
2 cup (250 grams) bleached, all-purpose flour, ½ teaspoon salt, 1¼ teaspoons baking powder, ¼ teaspoon baking soda
In the bowl of a stand mixer or in a medium mixing bowl if using a hand mixer, cream the butter and sugar on medium speed until it is light, about 3 to 5 minutes. Scrape down the bowl as necessary.
4 tablespoon unsalted butter, softened, ¾ cup (150 grams) granulated sugar
Add the bananas and beat until softened. Add the egg and vanilla and beat on medium speed for one minute.
2 cups very ripe bananas (3 to 4 medium bananas), 1 egg, 1 teaspoon vanilla
Add the dry ingredients and mix on low until just mixed. Do not over-mix.
Reserve ¼ cup of chocolate chips for the top of the banana bread, and add the remaining ¾ cup of chocolate chips to the batter. Mix by hand.
1 cup chocolate chips
Scrape half of the banana bread batter into the loaf pan.
Dollop ⅓ cup of Nutella onto the top of the batter in large spoonfuls, and use a knife or spatula to swirl the Nutella into the batter.
⅔ cup Nutella or other chocolate hazelnut spread
Top with the remaining batter and repeat the dollops and swirling with the remaining Nutella.
⅔ cup Nutella or other chocolate hazelnut spread
Scatter the reserved ¼ cup of chocolate chips on top of the swirled batter.
1 cup chocolate chips
Bake for 50 to 60 minutes on a rack in the middle of the oven until a toothpick or knife inserted into it comes out clean (you may need to check in a few places if you stick a toothpick into a chocolate chip). Check it at about 45 minutes and cover the banana bread with a foil tent if it is browning too quickly.
Cool in the pan for about 10 minutes and then turn onto a cooling rack. It can be sliced when warm, but it is even better after it has cooled, wrapped in foil, and the crust has softened a bit. Store at room temperature for up to one week.