Preheat your oven to 350°F and grab an 8x8 baking dish (or any baking dish that is 2 to 2.5 quarts).
Peel and slice the apples into ¼-inch to ½-inch slices.
In a large mixing bowl, stir together the granulated sugar, 1 teaspoon cinnamon, and 2 tablespoons all-purpose flour. Add the apple slices and toss until well coated. Pour the apple mixture into your prepared baking dish.
In another bowl, mix the oats, brown sugar, flour, and ½¼ teaspoon cinnamon until combined. Pour in the slightly cooled, melted butter and stir until all the dry ingredients are evenly coated and the mixture looks crumbly—everything should be moistened.
Sprinkle the crumble topping evenly on top of the apples, gently patting it down without packing it too tightly.
Bake for about 45 minutes, or until the top is golden brown and the apple juices are bubbling around the edges.
Let cool slightly, then serve warm apple crisp with a scoop of vanilla ice cream and a drizzle of caramel sauce, if you’d like!