Get all your ingredients ready and measure accordingly. Preheat the oven at 190 degrees Celsius. Get your oven dish ready too. I used a square 23 cm Le Creuset one. Link in the text above.
Start by making your filling. Peel your apples, core then and cut into small pieces. Small pieces mean it cooks quicker and tastes better too.
Into your oven dish, add in your blackberries, lemon juice, vanilla essence, cinnamon powder and caster sugar. Give this a mix and leave to one side.
Mix the dry ingredients of your crumble (apart from the oats).
Add in your cubed butter and with your finger tips rub it with the flour mixture until it is crumbly. Ensure there are no lumps of butter left and the mixture is one consistency.
Combine the oats to the mixture.
Place this evenly on top of your filling and using a fork poke the crumble.
Place the casserole in the oven and cook for 25 minutes. Carefully take it out and poke again with a fork. This is to ensure the crumble is cooked in the middle too and you do not get a floury stodgy topping.
Bake for a further 20 minutes until brown, golden and crispy. The edges should be bubbling too.
Serve hot with custard, cream or ice cream