In a mixing bowl, combine gluten-free multipurpose flour, almond flour, and kosher salt. Cut in softened unsalted butter and powdered sugar until the mixture resembles coarse crumbs. Add in an egg and mix until just combined. Shape the dough into a disc, wrap in plastic wrap, and refrigerate for at least 1 hour.

While the dough chills, peel and dice your apples into bite-sized pieces. In a large bowl, toss the diced apples with fresh lemon juice to prevent browning.

In a medium saucepan, melt unsalted butter over medium heat. Add the prepared apples and cook for about 3-4 minutes until slightly softened. Mix in brown sugar, cornstarch, cinnamon, nutmeg, and a pinch of salt, stirring often until the mixture is thickened and bubbling, about 2-3 more minutes. Remove from heat and let cool slightly.

In a separate bowl, combine gluten-free flour, brown sugar, chopped pecans, cinnamon, and a tiny pinch of salt. Cut in cubed unsalted butter until the streusel appears crumbly. Transfer the mixture to the refrigerator for about 15 minutes.

Preheat your oven to 350°F (175°C) while you prepare the crust in a tart pan. Once your hour is up, remove the dough from the fridge and press it evenly into the bottom and sides of the pan.

Spread the cooked apple filling evenly over the chilled crust, then drizzle caramel sauce generously over the apples. Sprinkle the chilled pecan streusel topping evenly over the caramel.

Bake in the preheated oven at 350°F (175°C) for 15 minutes, then increase the temperature to 375°F (190°C) and bake for another 5-10 minutes until the streusel is golden brown. Reduce the temperature back to 350°F and bake for an additional 32-38 minutes until set.

Once baked, remove the tart from the oven and let it cool for about 15 minutes. Drizzle additional caramel sauce on top before slicing and serving.