In a large mixing bowl, combine the gluten-free multipurpose flour, almond flour, and kosher salt. Cut in the softened unsalted butter and powdered sugar until the mixture resembles coarse crumbs. Add the egg and gently mix until just combined. Chill the dough for 1 hour in the refrigerator.

While the crust is chilling, peel and dice the apples. Toss them with fresh lemon juice to prevent browning.

In a large saucepan over medium heat, melt the unsalted butter. Add the prepared apples and cook for 5 minutes until they begin to soften. Sprinkle in the brown sugar, cornstarch, cinnamon, nutmeg, and salt. Stir well and cook for another 5 minutes until the mixture thickens.

In a medium bowl, combine the gluten-free flour, brown sugar, chopped pecans, and a pinch of cinnamon. Mix well before adding cold, cubed butter and blend until crumbly. Chill the streusel while preheating the oven.

Preheat your oven to 350°F. Grease a tart pan with cooking spray or butter. Roll out the chilled crust dough between parchment paper until about 1/4-inch thick, then transfer it into the tart pan.

Spread the cooked apple filling evenly over the prepared crust. Drizzle with caramel sauce and sprinkle the chilled pecan streusel on top.

Bake at 350°F for 15 minutes. Increase to 375°F and bake for another 5-10 minutes until streusel is golden. Lower to 350°F and bake for another 32-38 minutes until filling is bubbly.

Allow the tart to cool in the pan for about 15 minutes before serving. Drizzle with extra caramel sauce for added indulgence.