Cook the bananas still in their skins on the barbecue for 8–10 minutes as the heat from the embers begins to lose its fierceness, until the skins have blackened and the flesh is softened. Alternatively, bake for the same period in a preheated oven, 200°C (400°F), Gas Mark 6.
Split the skins lengthways and place a banana in its skin on each of 4 serving plates. Drizzle the rum inside the baked banana and sprinkle with the lime rind. Serve at once, with scoops of ice cream and the crumbled ratafia biscuits.