Preheat oven to 350°F and grease your baking dish.
Prepare the filling: In a large bowl, toss apple slices with lemon juice, white sugar, flour, cinnamon, and nutmeg. Spread in the baking dish.
Make the topping: In another bowl, mix flour, brown sugar, cinnamon, and salt. Cut in cold butter using fingers or a pastry cutter until crumbly.
Assemble: Sprinkle the topping evenly over the apple mixture. Do not press it down.
Bake uncovered for 40–45 minutes until the topping is golden and apples are bubbling.
Cool for 10–15 minutes before serving.