01 - Set oven to 350°F (180°C) to prepare for baking.
02 - In a large bowl, combine sliced apples with lemon juice, granulated sugar, cinnamon, nutmeg, and all-purpose flour. Toss gently to coat evenly.
03 - Place the apple mixture into a greased 9-inch baking dish, spreading it uniformly.
04 - In a separate bowl, mix together flour, cold diced butter, brown sugar, rolled oats, and salt. Rub the mixture with fingertips until it forms coarse crumbs.
05 - Sprinkle the crumble topping evenly over the apple filling.
06 - Bake in the preheated oven for 35 to 40 minutes until the topping is golden brown and the filling is bubbling.
07 - Allow to cool slightly before serving warm; optionally accompany with vanilla ice cream or custard.