In a large mixing bowl, combine gluten-free multipurpose flour, almond flour, and kosher salt. Cut in softened unsalted butter and powdered sugar using a pastry cutter until the mixture resembles coarse crumbs. Add an egg and mix until a smooth dough forms. Wrap the dough in plastic wrap and refrigerate for at least 1 hour to firm up.

While the crust chills, peel and dice your apples into small pieces. Toss them in a bowl with fresh lemon juice to prevent browning and brighten their flavor. Set the prepared apples aside.

In a medium saucepan over medium heat, melt some unsalted butter. Once melted, add the diced apples and cook for about 3-5 minutes, stirring occasionally until they start to soften. Stir in brown sugar, cornstarch, cinnamon, nutmeg, and salt. Cook for a few more minutes until the mixture thickens and the apples are tender. Remove from heat.

In a bowl, mix together gluten-free flour, brown sugar, chopped pecans, cinnamon, and salt for the streusel topping. Cut in cubed butter until the mixture becomes crumbly. Place the streusel in the refrigerator to keep it chilled.

Preheat your oven to 350°F (175°C). Once the oven is ready, roll out the chilled dough on a lightly floured surface until it’s about 1/8 inch thick. Carefully transfer the rolled dough into a tart pan, trimming any excess. Prick the bottom with a fork.

Spread the warm apple filling evenly over the prepared crust. Drizzle caramel sauce over the apple filling, letting it seep in. Sprinkle the chilled pecan streusel topping evenly across the apples.

Place the assembled tart in the preheated oven at 350°F for 15 minutes. Carefully remove any weights you may have used, then increase the temperature to 375°F and bake for an additional 5-10 minutes. Once done, turn the oven back to 350°F and continue to bake for another 32-38 minutes.

Remove the tart from the oven and allow it to cool for at least 15 minutes before serving. Drizzle extra caramel on top and slice into wedges. Serve warm.