You could also use a ready made crumble mix if you like as well as it does save time, but you’ll still need to bake it on top of the cake in the same way, and bake the spare in the same way as well!
This cake will last in an airtight container for up to 3-4+ days
You can freeze this cake for 3+ months if you want
Weigh your cooking apples after peeling, coring and chopping (that is the peeled and chopped weight), and cut them into roughly 2cm chunks so they hold their texture through the long bake.
If the tops or crumble start browning too quickly, loosely cover the tins with foil for the last 10 to 15 minutes of baking.