Preheat the oven to the specified temperature mentioned in the recipe. Grease or line a cake pan with parchment paper.
In a mixing bowl, whisk together the all-purpose flour, cocoa powder, baking soda, and salt until well combined.
In a separate bowl, cream together the softened butter and granulated sugar until light and fluffy.
Add the eggs one at a time to the butter-sugar mixture, beating well after each addition.
Mix in the mashed bananas and vanilla extract until thoroughly incorporated.
Gradually add the dry ingredient mixture to the wet ingredients, alternating with buttermilk. Begin and end with the dry ingredients, mixing until just combined. Avoid overmixing.
Pour the batter into the prepared cake pan, spreading it evenly with a spatula.
Place the pan in the preheated oven and bake for the specified time in the recipe or until a toothpick inserted into the center comes out clean.
While the cake is baking, prepare the Bananas Foster topping. In a skillet, melt the butter over medium heat. Stir in the brown sugar until it dissolves and the mixture becomes syrupy.
Add the sliced bananas to the skillet and cook until they are softened and coated in the caramel sauce. If desired, stir in the rum extract or rum and let the mixture simmer for a minute or two.
Once the cake is baked, remove it from the oven and let it cool in the pan for a few minutes. Then, transfer it to a wire rack to cool completely.
Once the cake has cooled, pour the Bananas Foster topping over the cake, ensuring an even distribution. Allow the topping to set before serving.
Optional: Garnish the cake with whipped cream, toasted nuts, or additional sliced bananas for added visual appeal and flavor.
Slice and serve the Bananas Foster Fudge Cake, savoring the decadent combination of flavors and textures.