Preheat oven to 350. Line 2 8-inch cake pans with parchment paper and spray with cooking spray.
Add the cake ingredients to a food processor or bowl of an electric mixer. Mix until smooth. Divide between the prepared cake pans.
Bake for 25-30 minutes or until the cakes are golden and the centers spring back when lightly pressed with your finger. Cool completely.
Caramel Frosting
Combine the sweetener, cream, and butter in a medium saucepan. Cook over medium, stirring frequently, until deep golden brown and thickened. Depending on the heat of your stovetop this can take 10-15 minutes. Watch it carefully. Remove from the heat and add the vanilla. Add the cream cheese and mix until it is melted and thoroughly incorporated. It helps to mix with an electric mixer. Cool for 10 minutes.
Pour ¼ of the caramel over the bottom layer of the cooled cake. Spread to the edges and let sit for 5 minutes. Add the top layer of cake. Slowly drizzle the caramel over the top. It helps to do this in 2 or 3 batches so it doesn't all drip down the sides. Simply spread a layer of caramel, let that cool, and then add another layer of caramel on top. If the caramel in the saucepan gets too cool you can reheat it over warm.
Serve immediately for a soft caramel frosting. When refrigerated this sets to be firm like a ganache.
Notes
This is rich so I kept the serving size small. A serving is 1/16th of the cake.
If you are making this cake in advance do not add the optional banana slices until right before serving. They do brown after some time in the fridge.