Preheat the oven to 350°F (175°C). Grease and line a 9x13 inch baking pan.
In a medium bowl, whisk together flour, baking soda, and salt.
In a large bowl, whisk melted butter, granulated sugar, and brown sugar until smooth.
Beat in the eggs one at a time, then stir in mashed bananas, sour cream, and vanilla.
Fold the dry ingredients into the wet mixture until just combined. Don’t overmix.
Pour the batter into the prepared pan and bake for 30–35 minutes, or until a toothpick comes out clean.
Let the cake cool slightly, then drizzle generously with salted caramel sauce before serving.