01 - Set the oven temperature to 350°F (180°C) to prepare for baking.
02 - In a large mixing bowl, combine sliced apples with granulated sugar, ground cinnamon, lemon juice, and all-purpose flour. Toss gently to coat evenly.
03 - Place the apple mixture into a greased 9-inch (23 cm) baking dish, spreading evenly.
04 - In a separate bowl, mix flour, rolled oats, brown sugar, and salt. Incorporate cold, diced butter by rubbing with fingertips until the mixture reaches a coarse breadcrumb texture.
05 - Evenly distribute the crumble topping over the apple filling in the baking dish.
06 - Bake for 35 to 40 minutes, until the topping is golden brown and the filling is bubbling through.
07 - Allow the dessert to cool slightly before serving. Enjoy warm, optionally accompanied by custard, cream, or vanilla ice cream.