Melt the butter in a wide pan over a medium heat. Slice the bananas in half lengthways, add to the pan and cook for 3–4 minutes, carefully turning once, until golden on both sides. Sprinkle over the sugar and cinnamon and heat gently to dissolve.
Pour in the rum and carefully ignite it with a long match to flambé the bananas. Allow the flames to die out while spooning the liquid over the fruit.
Arrange the bananas on warmed serving plates with a scoop of ice cream, then sprinkle with the pecans and serve immediately.