For the caramel, place the sugar and 6tablespoons of water in a medium-sized saucepan and allow to dissolve over a medium heat. Do not stir the caramel, but swirl the pan gently. Once the sugar has dissolved, boil rapidly until the caramel is a rich golden brown. Remove from the heat and stir in the butter. Add the cream (it will hiss!), vanilla seeds, rum and salt. Allow the caramel to cool a little, then add the brandy. Keep warm.
Toast the hazelnuts in a dry frying pan over a medium heat, shaking the pan to brown them all over. Tip out onto a saucer.
Add a good knob of butter to the frying pan and lay in the bananas, cut side down. Fry for 2–3 minutes before turning over and cooking the other side. Remove from the heat but keep warm.
Toast the brioche slices to a good brown and set each one on a plate. Briefly shake the pan of bananas over the heat to make sure they are hot and arrange them on the toast, pouring over any butter from the pan too. Sprinkle with the toasted hazelnuts, spoon over the warm caramel sauce and add a generous ball of ice cream.