Heat a heavy -based frying pan over medium heat. Add the butter, sugar and cinnamon and stir until the sugar dissolves into the butter. Add the bananas and cook for a few minutes or until they soften, then add the rum and tilt the pan to flambe.
Place 4 scoops of ice - cream into serving bowls. Add the hot bananas around the outside, then spoon a little of the sauce over the top. Serve immediately.