Preheat your oven to 350°F (175°C) and grease your loaf pan with cooking spray or butter to prevent sticking.
In a medium bowl, whisk together the all-purpose flour, baking soda, and salt. Set this mixture aside while you prepare the wet ingredients.
In a large mixing bowl, use a whisk or an electric mixer to cream the softened butter and granulated sugar together until light and fluffy. This should take about 3-4 minutes.
Crack in the eggs, one at a time, mixing well after each addition. Then, fold in the mashed ripe bananas until fully incorporated.
Add the plain yogurt (or sour cream) and vanilla extract to the banana mixture. Stir until everything is well combined.
Gradually add the dry ingredient mixture to the wet ingredients, stirring gently with a rubber spatula until just combined. Be careful not to overmix; a few lumps are perfectly fine.
Spoon half of the banana bread batter into the prepared loaf pan. Then, dollop half of the Nutella on top. Use a knife or skewer to gently swirl it into the batter. Repeat this process with the remaining batter and Nutella.
Place the loaf pan in the preheated oven and bake for 55-65 minutes, or until a toothpick inserted into the center comes out clean. If the top starts to brown too quickly, you can cover it loosely with aluminum foil.
Once baked, remove the banana bread from the oven and let it cool in the pan for about 10 minutes. Then, transfer it to a cooling rack to cool completely. Slice and enjoy your delicious Nutella Swirled Banana Bread!
