1.Grease 20cm round sandwich pan. Sift dry ingredients into large bowl, rub in butter. Add enough water to make ingredients cling together. Press dough into ball, knead gently on floured surface until smooth, cover and refrigerate for 30 minutes.
2.Roll two-thirds of the dough on lightly floured surface until large enough to line base and side of prepared pan. Lift pastry into pan, brush edge of pastry with a little milk.
3.To make the filling, peel, quarter, core and thinly slice apples. Combine apples, sugar, water, juice and nutmeg in a pan, bring to the boil and cover and simmer for about 10 minutes, or until apples are tender. Drain the mixture and cool, before spreading into prepare pastry case.
4.Roll remaining pastry until large enough to cover filling, place pastry over filling and press the edges together, trimming neatly. Brush pastry with a little more milk and cut two slits in the pastry.
5.Bake in a moderate oven for about 50 minutes or until lightly browned; cool cake in the pan before turning out.
6.To make the passionfruit icing, sift icing sugar into a small heatproof bowl. Stir in butter, passionfruit pulp and enough milk to make a stiff paste. Stir icing over hot water, until spreadable.
7.Top the cold Charlotte with passionfruit icing and leave to set before cutting.
This recipe can be made a day ahead; to store, cover and refrigerate. This recipe is not suitable for freezing or microwaving.