Preheat the oven to 160C, line a 20x 20cm square cake tin with parchment and a baking sheet with a layer of greaseproof paper.
Make a hard caramel first by place the granulated sugar in a deep, heavy based pan, melt the sugar, watching carefully and swirling often to make sure the sugar melts evenly, when all the sugar is melted and amber in colour pour onto the lined baking sheet and tilt it to spread the sugar layer over the sheet. Set aside to cool and then use a rolling pin to break in to small shards.
Place the butter in a pan and melt over a low to medium heat, once melted keep gently stirring the butter and gently brown it, there should be a nutty aroma and the milk solids in the butter should be golden brown. Then pour the browned butter into the bowl of a free standing mixer and allow to cool slightly.
Add the banana, sugars and vanilla to the bowl and beat for a few minutes with the paddle attachment until all the ingredients are incorporated. Then beat in the eggs one at a time.
Combine the flour and baking powder together and then add to the mixer bowl, beat until incorporated. Then stir through the pecans, milk chocolate and white chocolate.
Pour the mixture into the lined square cake tin. Add the halved sliced bananas to the top and sprinkle half of the cooled caramel shards over the top, reserving half for garnish.
Place in the oven and bake for 40-50 minutes until a cake tester comes out clean.
Allow to cool and sprinkle with the remaining caramel shards. Cut in to 8 slices and serve.