search the bbc site and you will find a recipe, they are very easy to make but I have to admit to sometimes buying the crumble topping which comes in bag in asda. you can either just slice some apples and put in a dish and sprinkle the topping over (the packet will give you timings etc) or you can stew your apples in a little bit of water for about 10 mins before if wanting softer. To make my packet one seem a bit more homemade i sometimes put a little orange grind over it.
I usually mix a couple of tablespoons of porridge oats with my crumble mix 8oz flour,4oz margarine or butter and 4oz sugar light brown sugar gives a nice flavourwhen you have worked the the flour , butter and sugar to resemble fine breadcrumbs stir in the oats.I usually cook my bramley cooking apples before putting on the crumble and it depends how sweet your tooth is a little sugar sprinkled on the top before cooking.
This is my Mum's legendary recipe(serves 4):
12oz self raising flour
4oz block butter/magarine cut into cubes (at room temperature)
4oz sugar plus extra for apples
6 large cooking apples
Slice apples and place in boiling water (with sugar added to taste) for about 5 minutes.
In the meantime rub the butter/margarine into the flour until it resembles breadcrumbs and stir in the sugar
Place the apples in the serving dish with a little of the juice and spoon the crumble mix on top
Cook at 180 c for 40 minutes
Serve with hot custard