• Preheat the oven to 350 degrees Fahrenheit (175 degrees Celsius). Grease an 11-by-7-inch pan with cooking spray.
• Arrange the bananas, cut-side-down, in the prepared pan and set aside.

Sauce

• In a large pan over medium-low heat, combine the butter, light brown sugar, salt, and cinnamon. Cook, stirring frequently, until the butter is melted, the sugar is dissolved, and the mixture is well-combined.
• Add the rum and bring the mixture to a simmer.
• Using a lighter, stand back and carefully ignite the rum.
• Shake the pan until the flames subside.
• Remove the sauce from the heat and pour over the prepared bananas. Set aside.

Cake

• In a large bowl, using a stand or a hand mixer, beat the butter, sugar, and light brown sugar together until creamy and lightened in color.
• Add the eggs, one at a time. Add the vanilla extract and buttermilk, and mix to combine.
• In a second large bowl, combine the flour, baking powder, baking soda, and salt.
• Add the wet ingredients to the bowl containing the dry ingredients, and mix until just combined, being careful not to over-mix the cake batter.
• Carefully spoon the cake batter over the bananas. Using an offset spatula or the back of a spoon, gently spread the batter, covering the fruit.
• Set an empty baking sheet on the bottom of the oven, or on a rack directly underneath where you will bake cake, to catch any foster sauce that may drip during baking.
• Bake the cake in the center of the oven for 30 to 40 minutes, or until a toothpick inserted into the center-bottom, near the bananas, comes out clean.
• Remove the cake from the oven and let the cake cool in the pan for 10 minutes.
• Use an offset spatula to ensure the sides of the cake are free from the pan. Place an upside-down plate or platter, large enough to hold the cake, on top of the cake pan. Carefully invert the cake onto the plate/platter to show off the caramelized bananas underneath.
• Let the cake cool for about 20 minutes before slicing and serving.