Put the apples and cranberries into a 1.5 litre (2½ pint), 5 cm (2 inch) deep ovenproof dish and sprinkle over the sugar and water. Cook, uncovered, in a preheated oven, 180°C (350°F), Gas Mark 4, for 10 minutes.
Put the butter, sugar, flour and eggs for the topping in a bowl, and beat together until smooth. Stir in the orange rind and juice.
Spoon the mixture over the partially cooked fruit and spread into an even layer. Return to the oven and cook for 30–40 minutes until the topping is golden and the centre springs back when pressed with a fingertip. Dust with sifted icing sugar and serve warm with custard or cream.