Preheat the oven to 180 degrees C
Put the flour and butter or margarine into a bowl
Rub the fat into the flour using your fingertips, until it looks like breadcrumbs
Stir in the sugar
Stir in the oats
Peel the apples and slice into chunks
Place in a casserole
Wash the blackberries in cold water and stir into the apples
Sprinkle the sugar over the fruit
Add the water
Spoon the crumble over the top of the fruit, ensuring an even covering
Bake in the preheated oven for about 45 minutes
Serve with custard, ice cream, evaporated milk or cream