Preheat the oven to 175C/350F
Grease (but do not line) a 20cm (8 inch) cake tin (NOT a springform tin)
Pour the caramel into the tin and spread over the base.
Place the egg whites into a clean bowl of a Kitchen stand with a whisk attachment fitted.
Whisk the egg whites on high until medium peaks form.
Slowly add the maple syrup whilst still whisking.
Add the banana, vanilla extract and continue to whisk.
Add the egg yolks one at a time until incorporated.
In a separate bowl, sift together the dry ingredients.
Add the dry ingredients to the wet and whisk on low to combine.
Add the water/milk and whisk on high.
Pour the cake mixture evenly over the caramel.
Bake for 40-50 minutes or until cooked through.
Remove from the oven and allow to rest for 10 minutes.
Run a knife around the edge of the tin and invert the cake onto a serving plate/tray.
If any caramel is stuck on the bottom of the tin, remove it and spread over the cake.
Can be served warm or cold.