1. Melt the butter in a large frying pan over a medium heat.
2. Add the bananas and cook for about 2 minutes, turning the slices once.
3. Tip in the sugar and stir until melted and lightly caramelised, then add the rum and allow to bubble. If you wish, carefully ignite with a match or a taper (if using a gas hob).
4. Serve when the flames have subsided, with crème fraîche, dusted with cinnamon if you wish.