Begin by preheating your oven to 350°F (175°C). This ensures that your apple crisp bakes evenly.
Take your peeled and sliced apples and place them in a large mixing bowl. Add the granulated sugar, ground cinnamon, and lemon juice (if using). Toss everything together until the apples are evenly coated. Set this aside to rest and let the flavors meld.
In a separate bowl, combine the graham cracker crumbs, granulated sugar, and melted butter. Mix until the crumbs are well moistened. Press this mixture firmly into the bottom of a 9x13-inch baking dish. This will form a delightful base for your apple mixture.
Once your apples have rested, layer them evenly over the prepared crust. Spread them out so that each bite has a mix of flavors.
In another bowl, combine the flour, rolled oats, brown sugar, cinnamon, and melted butter. Use a fork or your fingers to mix until you have a crumbly texture. Sprinkle this topping generously over the apple layer.
Place your dish in the preheated oven and bake for about 45-50 minutes, or until the topping is golden brown and the apples are bubbling. Keep an eye on it—each oven is different!
Once baked, allow it to cool slightly. Serve warm, drizzling with caramel sauce or a scoop of ice cream if desired. Trust me, you’ll be coming back for seconds.