Preheat the oven to 190°C (375°F).

In a large mixing bowl, combine sliced apples, blueberries, granulated sugar, cinnamon, and lemon juice.

Transfer the prepared fruit mixture into a 22cm (9-inch) ceramic baking dish, spreading evenly.

In a separate bowl, whisk together the flour, light brown sugar, and salt.

Incorporate the cold cubed butter into the flour mixture using a pastry blender or fingertips until the texture resembles coarse breadcrumbs.

Stir the rolled oats into the crumble mixture until evenly distributed.

Spread the crumble topping over the fruit base in an even layer.

Bake for 35 to 40 minutes, or until the topping is golden brown and the fruit filling is bubbling at the edges.

Remove from the oven and allow to rest for 10 minutes to set the juices before serving.