1. Preheat oven to 190°C/375°F/Gas 5.
2. Put the flour into a bowl, add in butter and rub into flour with your fingers.
3. Add in sugar and oats and mix together.
4. Prepare fruit. Stew apples/rhubarb if making apple/rhubarb crumble.
5. Put fruit in ovenproof dish. Spoon crumble over fruit. Bake in oven for about 20 minutes.

To Stew Apples/Rhubarb

1. Peel, core and roughly chop apples. Or clean, trim and slice rhubarb stalks into 1"/2½cm pieces.
2. Place in a saucepan with a sprinkling of sugar and a little water (3 tablespoons approx) over a low heat, stirring occasionally until softened. 
3. If liked, add a pinch of cinnamon/ginger to the apples/rhubarb when soft.