Preheat the oven to 350°F (180°C). Make sure your oven is fully heated before placing the bread inside, as an even temperature is crucial for proper baking.
Prepare your loaf pan. Grab an 8½x4½-inch loaf pan and spray it with baking spray that contains flour. This will help the bread release easily once it’s baked.
Line the pan with parchment paper, letting some excess hang over the sides. This acts as handles to lift the loaf out effortlessly once it’s done.
In a medium bowl, whisk together the flour, salt, baking soda, and baking powder. This step ensures that your leavening agents are evenly distributed throughout the flour.
In a large bowl, whisk together the mashed ripe bananas, brown sugar, oil, sour cream, eggs, melted butter, and vanilla. Mix until everything is well combined; the mixture should be creamy and consistent.
Gently stir in the flour mixture just until combined. Be careful not to overmix; you want to keep the batter light and fluffy, with no dry spots remaining.
Transfer one-third of the batter (about 1 cup or 281 grams) to a small bowl. Stir in ¼ cup of peanut chocolate spread.
Using a 1½-tablespoon spring-loaded scoop, scoop the batters into the prepared pan in an alternating pattern. This creates beautiful swirls once baked.
Spoon the remaining 2 tablespoons of peanut chocolate spread on top of the batter. Using a skewer or wooden pick, gently swirl the spread into the batter. Don’t overdo it; you want to see those lovely swirls!
Bake your loaf until a wooden pick inserted in the center comes out clean, about 1 hour to 1 hour and 10 minutes. Loosely cover with foil during the final 15 minutes of baking to prevent excess browning.
Once baked, let cool in the pan on a wire rack for 10 minutes. Using the excess parchment as handles, remove the loaf from the pan and let it cool completely on a wire rack. This cooling step is essential for the best texture.
Store in an airtight container for up to 3 days, if it lasts that long!