Preheat your oven to 350°F (175°C). Gather a ramekin or small baking dish.
Peel and slice your apple into thin, even slices, about ¼ inch thick. Place the slices in a small bowl.
In a separate bowl, combine 2 tbsp granulated sugar, ¼ tsp cinnamon, and ½ tbsp flour. Toss the apple slices in this mixture until they're evenly coated. Then, transfer the apple filling to the baking dish.
In a separate bowl, combine the oats, brown sugar, flour, and cinnamon. Then, stir in the slightly cooled melted butter until the mixture forms a crumbly topping.
Sprinkle the crisp topping evenly over the apples.
Bake for 25–30 minutes, or until the topping is golden and the apples are tender and bubbling.
Let cool slightly, then dig into your warm apple crisp! Serve warm with a scoop of vanilla ice cream or caramel sauce for the perfect finish.