Preheat the oven to 375℉ and prepare an 8x8” baking dish by greasing it with cooking spray or butter.
In a large bowl, add the peeled and chopped apples and the fresh blackberries. Pour in the lemon juice and white sugar overtop and toss gently. Try to ensure the fruit is coated with the sugar. Set aside while you work on the crumble.
In another large bowl, combine the flour, oats, brown sugar and cinnamon. Stir this together until it’s well combined.
Cut the cold butter into cubes and place into the crumble mixture. Using either a pastry blender, a butter knife or your hands, cut or combine the butter into the dry ingredients until it’s crumbly in texture.
Stir the fruit once more, place it into the prepared baking dish and spread out evenly. Pour the crumble mixture evenly over the apples and blackberries and use a spoon or knife to distribute over the fruit and into each corner of the dish.
Bake for 35-45 minutes, or until the crumble topping is golden brown and the fruit is bubbling. Allow this to cool for at least 10 minutes before serving. Enjoy!