Grease a standard 9x5-inch loaf pan with a little extra butter or cooking spray, or line it with parchment paper for easy removal.
In a medium bowl, thoroughly mash the 360g of bananas (about 3 large or 4 medium bananas) with a fork until smooth. Set aside.
In a large mixing bowl, cream together the 1/2 cup of butter and 1 cup (200g) of sugar until the mixture is light and fluffy.
Add the 2 beaten eggs and 1 tsp of vanilla extract to the butter-sugar mixture. Mix well.
Stir in the mashed bananas and 1/2 cup of buttermilk until completely combined.
In a separate bowl, whisk together the 240g of flour, 1 tsp of baking soda, and 1/2 tsp of salt.
Gently fold the dry ingredients into the wet banana mixture. Stir just until combined—be careful not to overmix, or the bread will be tough.
If you are using them, gently fold in the 1/2 cup of chocolate chips or 1/2 cup of nuts now.
Pour the batter into your prepared loaf pan and smooth the top.
Bake for 60 to 70 minutes, or until a toothpick inserted into the center comes out clean or with just a few moist crumbs.
Let the banana bread cool in the pan for about 10 minutes, then transfer it to a wire rack to cool completely before slicing.
Baking Secrets
Toss the chips or nuts in a pinch of flour before folding them into the batter to keep them from sinking to the bottom of the loaf pan while baking.
If you don't have buttermilk on hand, you can make a quick substitute by adding 1.5 teaspoons of lemon juice or white vinegar to 1/2 cup of regular milk and letting it sit for 5 minutes.