Preheat the oven to 180°C/ 350°F/Gas mark 4.
Core the apples and score through the skins around the middle with a sharp knife.
Put the apples in a wide ovenproof dish, and spoon 1 tablespoon marmalade into the centre of each. Cover and bake in the oven for 35–40 minutes until tender.
Whisk the egg whites in a large bowl until stiff enough to hold soft peaks. Whisk in the sugar, then fold in the remaining marmalade.
Spoon the meringue over the apples, then return to the oven for 10–15 minutes. Serve immediately.