This is a very simple and delicious way to use up bananas and filo pastry.

4-6 sheets of filo pastry (or use puff pastry)
100 g brown sugar
75 g butter
3 ripe bananas, sliced (make circles or diagonal shapes, up to you)
50 g chopped hazelnuts (or any nuts, chopped, flaked or sliced)
orange zest, optional

Preheat oven to 180C. You need an ovenproof frying pan. Place frying pan on top of your filo sheets and cut a circle about 2 cm wider than your pan. Don't discard the cutoffs, you'll use them as well.
Place the pan on medium heat and melt the brown sugar and butter. Once the sugar has dissolved, turn up the heat and let the caramel thicken and darken. It will only take 4-6 minutes. Swirl the pan occasionally but don't take your eyes off it as it can burn quickly. 
Take off the heat and arrange the banana slices on top of the caramel in a nice pattern. Sprinkle over nuts and zest, if using. Lay your pastry on top, and the extra pieces, and tuck in the sides. Cut a slit in the top for the steam to escape.
Bake for around 25 minutes until the top is browned and crispy. Puff pastry will take a little longer.
Leave to cool for a few minutes before turning out onto a serving plate, using gloves to hold the hot pan handle and the plate.
Best served with ice cream!