Preheat oven to moderately hot (200°/180° fan forced). Grease shallow 2.5 litre (10cup) ovenproof dish.

Peel, core and halve apples; cut each half into four wedges. Melt butter in large frying pan; cook apple, stirring, about 5 minutes or until browned lightly. Add brown sugar; cook, stirring, about 5 minutes or until mixture thickens slightly. Place apple mixture into prepared dish; cool 5 minutes.

Meanwhile, combine caster sugar and flours in medium bowl; make well in centre. Gradually whisk in combined remaining ingredients until smooth. Pour batter over apple mixture; bake, uncovered, about 40 minutes.

Serve hot with double cream; dust with icing sugar, if desired.