Peel and chop the apples in small cubes. Mix the sugar and cinnamon with the apples and pour into the baking tin.
Making the crumble
I like to make the crumble with my hands. Put all the ingredients in a bowl at once. Rub the butter between your fingers and knead into a firm but crumbly dough.
The dough will eventually (or just about) form a firm, cohesive dough. Then it is good. Sprinkle the crumble over the apple mixture.
Baking the crumble
Bake the crumble for 30 minutes at 200°C/400˚F (conventional oven).
How to store
Store in the fridge, covered, for up to 3 days. I have not frozen this but it should be fine in an airtight container.