Preheat the oven to 350°F and line a 9x9-inch baking pan with parchment, leaving an overhang on two sides. Mix the graham cracker crumbs, brown sugar and melted butter, press into the pan and bake for 10 minutes. Reduce the oven to 325°F.
Melt the butter in a skillet over medium heat, add the diced apples, brown sugar and cinnamon and cook for 5 to 6 minutes until tender and the juices have cooked off. Let the apples cool slightly.
In a bowl, mix the flour, oats, brown sugar and cinnamon for the streusel. Rub in the cold butter with your fingertips until it forms pea-sized clumps, then refrigerate until needed.
Blend the cottage cheese in a food processor or blender for 2 to 3 minutes, scraping down the sides, until completely silky.
Add the cream cheese, sugar, cornstarch and vanilla and blend until smooth. Add the eggs and pulse just until combined.
Pour the cheesecake batter over the crust, scatter the cooked apples evenly on top and sprinkle with the streusel. Bake for 45 to 50 minutes, until the streusel is golden and the center has a slight wobble.
Cool completely in the pan, then refrigerate for at least 4 hours. Lift out using the parchment, cut into 16 bars, drizzle with caramel sauce and finish with a pinch of flaky sea salt.