1. Grease a 9 inch removable bottom tart pan and preheat the oven to 350°F (175°C).

2. Make the crust by whisking together the gluten-free flour blend, almond flour, granulated sugar, cinnamon, and salt in a mixing bowl.

3. Cut the cold butter into the dry ingredients with a pastry cutter or your fingertips until the mixture resembles coarse crumbs with a few pea sized bits of butter remaining.

4. Stir in the beaten egg, then add just enough ice water for the dough to hold together when squeezed in your hand.

5. Transfer the dough to the tart pan and press it evenly over the bottom and up the sides, smoothing the surface with lightly floured fingers or the back of a spoon.

6. Chill the pressed crust in the refrigerator for 20 minutes to firm up and prevent shrinking.

7. Dock the chilled crust all over with a fork, line with parchment, fill with pie weights or dried beans, and par bake for 12 to 15 minutes until the edges are just turning golden.

8. Carefully remove the parchment and weights and bake the bare crust for 5 more minutes to dry the bottom, then set the pan on a wire rack while you prepare the filling.

9. For the creamy filling, beat the softened cream cheese with an electric mixer until completely smooth, then blend in the brown sugar until no lumps remain.

10. Mix in the sour cream, egg, vanilla, and salt just until combined and silky, scraping down the bowl as needed.

11. Pour the filling into the warm par baked crust and smooth it into an even layer with an offset spatula.

12. For the apple layer, toss the sliced apples with lemon juice, brown sugar, cinnamon, and nutmeg in a large bowl until all slices are evenly coated.

13. Arrange the apples in slightly overlapping concentric circles over the filling, starting at the outer edge and working toward the center to create a fan pattern.

14. To make the crumble topping, stir together the gluten-free oats or almond flour, brown sugar, chopped nuts, melted butter, and a pinch of salt until clumpy.

15. Sprinkle the crumble mixture over the center of the tart, leaving the outer ring of apples mostly exposed.

16. Bake the tart for 30 to 35 minutes, or until the filling is mostly set with a slight jiggle in the center and the apples are tender.

17. If the crust or apple tips begin to brown too quickly, tent the tart loosely with foil for the last 10 minutes of baking.

18. Transfer the tart to a wire rack and cool completely, at least 1 to 2 hours, so the filling finishes setting and slices cleanly.

19. Shortly before serving, warm the caramel sauce until pourable and drizzle it generously over the apples and crumble.

20. Dust the crust edge with powdered sugar if desired, slice into wedges, and serve plain or with vanilla ice cream or softly whipped cream.