Preheat your oven to 350°F (175°C). Grease a 4×8-inch loaf pan with butter or non-stick cooking spray to ensure easy removal. In a large mixing bowl, peel the ripe bananas and use a fork to mash them until they are smooth with just a few small chunks remaining for texture.
Pour the melted butter into the mashed bananas and stir well. Mix in the granulated sugar, brown sugar, beaten egg, and vanilla extract until fully combined. Sprinkle the baking soda and salt over the mixture and stir. Finally, gently fold in the flour. Stop mixing as soon as the flour streaks disappear to keep the bread tender.
Pour the batter into your prepared loaf pan and smooth the top with a spatula. Place the pan in the center of the oven and bake for 50 to 60 minutes. Test for doneness by inserting a toothpick into the center; it should come out clean or with just a few moist crumbs. Remove the bread from the oven and let it cool in the pan for 10 minutes before transferring it to a wire rack to cool completely.