Take 150g of caster sugar, add enough water to cover and on a low heat reduce the syrup until golden grown. Take off the heat and add the butter and cream mix until you have your creamy caramel sauce.
TIP: if your syrup turns to crystals, add some boiling water, if it continues, just keep adding the water, it will eventually turn to golden syrup. Just takes longer but saves your sanity from starting from scratch!
Let the caramel cool a little. I've used a loaf tin for this recipe. Pour the caramel, about 1 cm in the base. Cut up the last banana, and layer, then pour on the cake batter.
Don't worry of the caramel comes up the side, it will do that.
Bake in the middle of the oven for 50 minutes. The caramel will be bubbling up the side and the top will be brown. Tap the top of the cake and you will feel it's cooked if taps hollow.