Peel and core the apples then slice or dice to your preferred size (I go for about a 2cm square dice, if you prefer big chunks of apple cut them into larger chunks or thicker slices). Add the sugar and cinnamon, and the flour if you don’t want the apples to be too juicy. Stir together and place into your dish (see notes) pouring over any sugar cinnamon mixture that doesn’t cling to the apples.
For the topping
Melt the butter on the hob or in the microwave.
Mix the rest of the ingredients together then stir in the melted butter.
Now stir in 50ml of cold water. The mixture should look clumpy and all the flour and oats should be damp.
Sprinkle the topping over the fruit then place in the oven and cook for 35-40 minutes. The topping should be golden and the apples soft and gently bubbling.
The dish I used for this was 20x23cm and 5cm deep. You can cook this in any shaped dish as long as it has a similar volume. If you’re not sure then tip in the apples and give it a go. The crumble topping is about 1/3 the volume of the apples.