In a medium bowl, combine graham cracker crumbs, melted unsalted butter, and granulated sugar until well mixed. Line a muffin pan with paper liners, then evenly press about 1 tablespoon of the mixture into each liner. Bake at 350°F (175°C) for 5 minutes. Allow to cool slightly.

In a large mixing bowl, beat the softened cream cheese, granulated sugar, egg, and vanilla extract together until smooth and creamy. Spoon the cheesecake mixture over the pre-baked crusts and create a smooth top. Set aside.

In a skillet over medium heat, melt 1 tablespoon of butter, add diced apples, brown sugar, and cinnamon. Cook for 3-4 minutes until apples are tender. Let cool before adding to cheesecakes.

In a mixing bowl, combine rolled oats, flour, brown sugar, melted butter, and salt. Mix until crumbly. Sprinkle topping over each cheesecake once apple filling has cooled.

Bake the mini cheesecakes for 18-20 minutes. Look for a slight jiggle in the center and a golden-brown topping. Remove from the oven and cool.

Transfer the mini cheesecakes to the refrigerator and chill for at least 2 hours before serving.

When ready to serve, carefully remove the mini cheesecakes from the muffin liners and top with whipped cream or caramel sauce.