Adding sour cream to banana bread batter improves its texture and taste. Sour cream makes the bread more moist and slightly spongier compared to using regular milk. It also improves the texture of other baked goods like sponge cakes. Sour cream has a higher fat content, which weakens the gluten strands in flour and makes the batter stretchy and easier to work with. If you don't have sour cream, you can use alternatives like Greek yogurt or buttermilk. Nutella can be added for extra flavor.