Peel the apples with the peeler and dice them up.
Place the diced apples in a pan with a little bit of water and 2 tablespoons of sugar. Let them cook on medium heat for about 10 minutes or till the apples are soft-ish. Don't let them get too soft because they'll also spend some time in the oven.
While the apples are cooking, place the flour in the bowl. Dice the cold butter in small bits and place it over the flour.
With the tips of your fingers start rubbing the butter and the flour together until it looks like wet sand. Add 1 or 2 tablespoons of sugar (depending on how sweet you want it to be) and the oats (these are optional) and mix them with the crumble.
Place the cooked apples in a tray (mine was a small square 45cmx45cm) and sprinkle the crumble on top. Make sure that the apples are covered but the crumble is not in a thick layer.
Place the tray in a pre-heated oven at 180 degrees Celsius and leave it for about 30 minutes or until the crumble is golden brown.
When it is done serve it with vanilla ice-cream (heavenly). If you want to stay away from ice-cream (why would you?!) I have a healthier alternative. Creme Fraiche aka sour cream. A surprising combination that actually works.