Preheat oven to 180°C Lightly grease a 6-cup capacity ovenproof dish. Place apples, 1/4 cup sugar and 2 tablespoons cold water in a saucepan. Stir over low heat until sugar dissolves. Increase heat to medium. Cook, stirring occasionally, for 10 to 12 minutes or until apples are tender but still holding their shape. Pour into prepared dish.
Using an electric mixer, beat eggs until pale. Gradually add remaining 1/4 cup sugar, beating until mixture is thick. Sift flours and custard powder together over egg mixture. Fold in until just combined.
Spoon mixture over apples. Bake for 20 minutes or until light golden.