Pour the crumb mix over the apples to form a pile in the centre, then use a fork to even out. Gently press the surface with the back of the fork so the crumble holds together and goes crisp, then lightly drag the fork over the top for a decorative finish. Sprinkle the oats and demerara over evenly, if you wish.

Set on a baking tray and put in the preheated oven for 35-40 minutes, until the top is golden and the apples feel very soft when you insert a small, sharp knife. Leave to cool for 10 minutes before serving.