In a large mixing bowl, combine gluten-free multipurpose flour, almond flour, and kosher salt. Work in softened unsalted butter and powdered sugar until the mixture resembles coarse crumbs. Add the egg and mix until a smooth dough forms. Shape the dough into a disk, wrap it in plastic wrap, and chill in the refrigerator for 1 hour to firm up.

While the dough chills, peel and dice your choice of sweet and tart apples into bite-sized pieces. Toss them with fresh lemon juice to coat and prevent browning.

In a skillet over medium heat, melt unsalted butter. Add diced apples and sauté them for 3 to 5 minutes until slightly softened. Sprinkle in brown sugar, cornstarch, cinnamon, nutmeg, and salt, stirring until thickened.

In a separate bowl, mix gluten-free flour, brown sugar, chopped pecans, cinnamon, and a pinch of salt. Cut in cubed unsalted butter until crumbly. Refrigerate until ready to assemble.

Preheat your oven to 350°F (175°C). Roll out the chilled tart dough into a circle about 1/8 inch thick and transfer it to a tart pan. Poke holes with a fork to prevent bubbling.

Spread the cooled apple filling evenly over the prepared crust. Drizzle generously with caramel sauce, then sprinkle with pecan streusel.

Bake at 350°F for 15 minutes, then remove weights and parchment. Increase the temperature to 375°F and bake for an additional 5-10 minutes until the streusel is golden. Reduce back to 350°F and bake for 32-38 minutes until set.

Allow the tart to cool at room temperature for 15 minutes. Drizzle with additional caramel sauce before serving warm.