Gather the ingredients including apples (such as Granny Smith or Honeycrisp), lemon juice, granulated sugar, ground cinnamon, ground nutmeg, all-purpose flour, old-fashioned rolled oats, brown sugar, salt, and unsalted butter.
Preheat your oven to 350°F (175°C) and lightly grease a 9x13 inch baking dish or a similar-sized oven-safe dish.
Peel, core, and slice the apples into thin wedges. Place the sliced apples in a large mixing bowl and toss them with lemon juice to prevent browning.
Sprinkle the granulated sugar, ground cinnamon, and ground nutmeg over the sliced apples, and toss to coat evenly.
In a separate mixing bowl, combine the all-purpose flour, old-fashioned rolled oats, brown sugar, and a pinch of salt. Cut in the unsalted butter using a pastry cutter or your fingers until the mixture resembles coarse crumbs.
Spread the coated apple slices evenly in the prepared baking dish. Sprinkle the crisp topping mixture over the apples, covering them completely.
Place the baking dish in the preheated oven and bake for 40 to 45 minutes, or until the topping is golden brown and the apples are tender when pierced with a fork.
Remove the apple crisp from the oven and let it cool for a few minutes before serving. Serve warm, optionally with a scoop of vanilla ice cream or a dollop of whipped cream on top.