Measure the amount of apples without the core or skin. Grate the apples for the recipe. I used the shredder attachment for my KitchenAid stand mixer on speed one but you can use a regular grater.
Use a whisk or a stand mixer with the beating accessory to mix the butter, sugar, oil, cinnamon, salt and baking powder until you have a homogeneous mix.
Add the egg and milk and mix again.
Incorporate the oats and flour using a spatula or continue using the beating accessory on your stand mixer.
Finish by mixing in the apples.
Put the paper liners inside the mould and fill up leaving about 3mm without dough.
Put the crumble on top of the dough separating it with your fingers as you do so.
Take to a preheated oven at 180C / 350F for 15-20min or until you can insert a skewer or sharp knife inside and it comes out without any dough