Preheat the oven to 350°F and line a 9-inch baking pan with parchment paper so that it hangs over the two longest sides. Grease the parchment paper with cooking spray.
In a large bowl, mash the bananas with a fork or spatula until they are softened. Add the buttermilk, eggs, vegetable oil and vanilla extract and whisk until combined.
Add the flour, sugar, baking soda and salt, and using a spatula, stir just until combined.
Fold in your preferred mix-in then transfer the batter to the prepared loaf pan.
Bake the banana bread for 55-60 minutes until a toothpick inserted comes out clean. Remove the banana bread from the oven and allow it cool for 20 minutes in the pan before using the parchment paper overhangs to lift the loaf out of the pan.