Preheat oven to 350°F (175°C). Grease a 9x9-inch baking dish.
Peel, core, and thinly slice the apples. Toss them in a large bowl with sugar, flour, lemon juice, and cinnamon. Spread evenly in the baking dish.
In a separate bowl, mix flour, brown sugar, salt, and nutmeg. Cut in cold butter using a fork or pastry cutter until the texture looks like coarse crumbs.
Sprinkle the crumble mixture over the apples without pressing down.
Bake for 40–45 minutes or until the top is golden and the edges are bubbling.
Cool for 10 minutes before serving. Top with vanilla ice cream or whipped cream if desired.
