- Place the apples into the base of an ovenproof dish.
- Rub together the flour and butter until the mixture resembles fine breadcrumbs.
- Stir in sugar.
- Sprinkle the crumble mixture over the apples.
- Bake at 190°C/375°F/Gas Mark 5 for 15 -20 minutes or until the crumble is golden.
- To make the custard, place the custard powder into a large measuring jug and add the boiling water. Stir briskly with a whisk until smooth and creamy.
- Serve the hot crumble with custard.