Line and grease desired cake pan (I used round).
To make the topping, melt the butter, brown sugar, and golden syrup (or maple syrup) together. Spread evenly in the cake pan. Slice the bananas and place layered over the sauce in a circular pattern.
In a large bowl mix together the mashed banana, oil, egg, custard, sugar, and syrup. Stir in baking powder, salt, and flour and mix until no lumps.
Pour the mixture over the caramel, banana topping, and spread out evenly.
Raise up on egg rings or foil balls in your slow cooker and cook on high for approximately 2 hours, with a tea towel under the lid. Cake is cooked when a skewer comes out clean. The topping will bubble up over the cake, then settle again as it cools.
Allow to cool in the tin for approximately 20 mins and then turn out onto a serving plate. Best served warm with custard, cream or vanilla Ice Cream.
