01 - Preheat oven to 350°F. Lightly grease a 9-inch baking dish.
02 - In a large bowl, toss sliced apples with granulated sugar, ground cinnamon, lemon juice, and all-purpose flour until evenly coated. Spread apple mixture evenly in the prepared baking dish.
03 - In a separate bowl, combine all-purpose flour, rolled oats, packed light brown sugar, ground cinnamon, and salt. Add cold diced butter and blend with fingertips or a pastry cutter until the mixture forms coarse crumbs.
04 - Distribute the crumble topping evenly over the apple filling.
05 - Bake uncovered for 40 minutes or until the crumble is golden and apples are bubbling.
06 - Allow to cool slightly before serving. Enjoy warm, optionally with vanilla ice cream or whipped cream.