Place the sourdough (crusts and all) into the Thermomix bowl and mill 10 sec/speed 10.
Add almost all the macadamias, leaving out a few for garnish. Blend 3 sec/speed 6.
Meanwhile, heat the butter in a frying pan on a medium heat, until melted. Add the crumb mixture to the hot butter and stir until crisping up and fragrant but not changing colour too much. This should take around 8 minutes.
Add the vanilla, cinnamon and cinnamon bark oil if using and keep stirring until all absorbed. Set aside,
Preheat oven to 180°C.
Make the Banana Caramel as per recipe. You could use the same skillet you are using to bake the entire dessert for this process.
When fully cooked, top this mixture whilst still hot with the crumb mixture piling it up as high as it needs to be. I used a 15cm skillet for this recipe and had about just under half the crumbs left over, which I will use with another fruit crumble recipe in the future.
Top with the reserved macadamias and bake for 15 minutes until golden and fragrant.
Serve with loads of vanilla ice cream.