Preheat your oven to 350°F (175°C) to ensure it's ready when you need to bake the apple crisp.
Peel, core, slice apples. Toss with sugar, flour, cinnamon. Coat evenly. Sweeten, flavor, thicken juices as they cook.
Mix oats, flour, brown sugar, cinnamon, salt. Cut in butter until crumbly. This forms the crisp topping.
Grease a cast-iron skillet with butter or cooking spray to prevent the apple crisp from sticking. You can also use a baking dish if you don't have a skillet.
Spread the coated apple slices evenly in the skillet.
Sprinkle the crisp topping evenly over the apples, covering them completely.
Place the skillet in the preheated oven and bake for 40-45 minutes, or until the topping is golden brown and the apples are tender. You can insert a fork or knife into the apples to check for tenderness.
Once baked, remove the skillet from the oven and let it cool for a few minutes. Serve the skillet apple crisp warm, either on its own or with a scoop of vanilla ice cream or a dollop of whipped cream for extra indulgence. Enjoy!