Heat a frying pan over a medium heat and cook the butter, sugar and cinnamon until the sugar has melted.
Stir in the banana liqueur, then add the banana pieces and cook, stirring carefully, until softened and beginning to turn golden-brown.
Add the rum and stir to combine. Turn up the heat and carefully flambé the rum until the flames die out.
To serve, place a scoop of ice cream onto four serving plates. Top with the banana pieces and pour over the sauce from the pan.