Preheat your oven to 350°F (175°C) and prepare a loaf pan by greasing it or lining it with parchment paper.
In a medium bowl, mash the ripe bananas. In a larger bowl, whisk together melted butter, white sugar, brown sugar, eggs, vanilla extract, buttermilk, and mashed bananas.
In another bowl, mix flour, baking soda, baking powder, salt, cinnamon, and nutmeg.
Gently fold the dry mixture into the wet mixture until just combined. Swirl in one tablespoon of caramel syrup.
Pour the batter into the prepared pan and bake for 55-65 minutes or until a skewer comes out clean.
Cool in the pan for about 10 minutes before transferring to a wire rack. Drizzle with remaining caramel syrup and sprinkle with sea salt.