Preheat oven to 350°F and arrange the rack in the center. Generously grease and line a 9x5-inch loaf pan with parchment paper. It's very important all the ingredients are the same temp so pull out the eggs and Greek yogurt and set aside. Melt butter in microwave and set aside to return to room temperature.
Remove the peels and place the bananas in a small bowl. Mash the bananas with a fork. We're going for a thick slightly chunky mash. Measure mashed bananas to get an exact and leveled 1-3/4 cups.
In a very large bowl, add the mashed bananas, 1 cup tightly packed brown sugar, room temp eggs, room temp yogurt, and vanilla extract. Use a hand whisk to briskly whisk until smooth.
While whisking constantly, slowly stream in the butter and oil. Whisk a few times after until mixture is fully emulsifed and smooth.
Add salt and baking soda. Whisk until incorporated then add in the flour. Whisk a few times then mix with a spatula just until no dry streaks of flour remain. Do not over mix here.
Pour half of the batter into the prepared loaf pan and smooth it into an even layer with the spatula. Warm Nutella in the microwave for 20 seconds and drizzle 3 tablespoons right on top. Use a butter knife to gently swirl into the batter. Pour remaining batter on top and smooth into an even layer. Drizzle remaining 2 tablespoons Nutella on top and gently swirl with a butter knife.
Place the bread on a sheet pan. Bake for 70-80 minutes (wide variance depending on the pan you use, actual heat of the oven, humidity, etc.), until lightly golden brown on top, bread springs back when you press it, and a toothpick, when inserted in the center, comes out clean or with moist crumbs. If needed tent the bread with foil and continue baking until toothpick comes out with moist crumbs or clean. My oven finishes it perfectly at 75 minutes.
Remove the bread and allow it to cool in the pan for 15 minutes before inverting onto a cooling rack to finish cooling. Don't rush the cool, the residual heat is finishing up the bread! Once cooled for about an hour, slice with a very sharp serrated knife. Enjoy!
Notes
Note 1: Be sure to use the right size loaf pan (9x5 inch) for best results. This bread doesn’t bake up nicely in smaller pans.Note 2: Let the bread sit in the pan for 10–15 minutes after baking. The bananas and sugar caramelize and create some gooeyness, so resting helps the loaf finish “baking” and firming up before slicing.Cool the bread on a wire rack so air can circulate. Run a knife around the edges and flip it onto the wire rack. If it’s not lifted, moisture can build underneath and make the bottom damp.Storage: Store any leftover bread in an airtight container at room temperature. Best eaten within 3 days.