Preheat the oven to 350°F (180°C).

Peel and core the apples, then cut them into approximately ½-inch (1.5 cm) cubes.

Place the chopped apples in a large mixing bowl.

Sprinkle the all-purpose flour, granulated sugar, and cinnamon over the apples.

Pour in the fresh lemon juice and toss thoroughly until the apple pieces are evenly coated.

Transfer the apple mixture to a 1½-quart baking dish and spread it into an even layer.

To prepare the topping, add the rolled oats, flour, brown sugar, baking powder, cinnamon, and salt to a separate bowl.

Pour in the melted butter and mix until everything is moistened and chunky crumbs begin to form. The mixture should resemble coarse, damp sand with plenty of small clumps.

Sprinkle the crumble mixture evenly over the apples. Use your fingers to gently break larger pieces into smaller clusters if necessary.

Bake the Apple Crumble for approximately 30–40 minutes, until the topping is deep golden brown and the apple filling is hot and bubbling around the edges.

Remove the baking dish from the oven and loosely cover it with foil.

Rest for approximately 10 minutes. This gives the hot apple juices time to thicken slightly before serving.

Spoon the warm crumble into bowls and serve with vanilla ice cream.