Preheat and prep the pan: Heat your oven to 350°F (175°C). Lightly butter a 9-inch square baking dish or similar 2-quart dish so the crisp doesn’t stick.

Peel and slice the apples: Peel if you like a softer texture, or leave skins on for more fiber and color. Core and slice into thin wedges, about 1/4 inch thick, so they cook evenly.

Season the apples: Toss the slices with 1 teaspoon ground cinnamon and 2–3 tablespoons brown sugar in the baking dish. If you have it, a squeeze of lemon brightens the flavor and helps balance sweetness.

Make the topping: In a bowl, combine 1 cup rolled oats and 1/2 cup packed brown sugar. Add 6 tablespoons melted butter and stir with a fork until the mixture looks like damp, crumbly sand. If using, add a pinch of salt to sharpen flavors.

Assemble: Spread the oat mixture evenly over the apples, pressing gently so some crumbs clump together. Don’t pack it too tightly—you want airflow for crispness.

Bake: Place the dish on the center rack and bake for 35–45 minutes. It’s done when the topping is deep golden and the apples are bubbling and tender when pierced with a knife.

Rest before serving: Let it cool for 10–15 minutes. This helps the juices thicken slightly so every spoonful is saucy but not soupy.

Serve: Enjoy warm on its own or with vanilla ice cream, whipped cream, or a drizzle of heavy cream.