Prepare the salted caramel first as it takes time to cool down and you will need it at room temperature before you can make the sponge or butter cream. Here it the link to my salted caramel recipe: Salted Caramel Recipe
Combine your wet ingredients and add the brown sugar, cream with a hand mixer or stand mixer. Combine the Flour, baking powder and salt. While mixing the wet ingredients gradually whisk in the flour mixture until well combined. Don't over mix to avoid activating gluten. Separate the batter into two equal parts.
Mash two cups or 450 grams of ripe bananas, add them to your cake batter (half of the portion) and blend with a rubber spatula or beater attachment. Flour an 8 inch or 20 CM cake form and place the batter in the form.
Fold 1 Cup of Salted Caramel sauce in to the remaining batter, place in a second cake form. Now bake both cake's at 180 C or 320 F for apx 45 minutes or until a toothpick comesy out of the center.
If you want a perfectly smooth cake then a cake turntable will definitely help, you can however get a nice finish simply using a palette knife or spatula. Alternate cake layers and connect them with a thick layer of buttercream frosting. When you are done cover the outer cake with a very thin layer of buttercream and place in the fridge for 20-30 minutes. This will lock in all the crumbs and allow you to get a smoother clean finish. When the buttercream has set, apply the final layer and decoration. You can add crushed digestive biscuits, caramel sauce and even some banana slices. Dip the Banana in caramel to avoid browning.