Place the sponge flan case in an ovenproof pie dish. Drizzle over the apple juice or chocolate liqueur, then spoon on the jam and spread it over evenly.
Run a blunt knife around the sides of the ice cream to help loosen it from the tub. Upturn the ice cream on top of the sponge flan case. Place on a flat surface in the freezer.
Whisk the egg whites in a grease-free bowl (if you see any yolk, remove it with a teaspoon) until they turn white and thick. Lift up the bowl and tip it slightly from side to side; if they don't move, they are ready. Whisk in 1 tablespoon of the sugar at a time until the meringue is smooth, glossy and stiffly peaking.
Spread the meringue over the prepared ice cream base using a palette knife, making sure the ice cream is completely covered and the meringue seals the edge of the sponge flan case. Return to the freezer for at least 1 hour (you can leave it for up to a day).
Bake in a preheated oven, 220°C (425°F), Gas Mark 7, for 5 minutes until the meringue is just starting to get tinged with brown, then serve immediately.