In a mixing bowl, combine gluten-free multipurpose flour, almond flour, and kosher salt until well blended. Cream together the softened unsalted butter and powdered sugar in a separate bowl until smooth and fluffy, about 2-3 minutes.

Add in the egg, blending until creamy. Gradually incorporate the flour mixture, stirring until a cohesive dough forms. Shape into a disk, wrap in plastic wrap, and chill for at least one hour.

Peel and dice the apples into bite-sized pieces, then toss them with fresh lemon juice to prevent browning.

In a sauté pan over medium heat, melt the butter and add the diced apples, cooking for 3-5 minutes until they soften.

In a separate bowl, mix together brown sugar, cornstarch, cinnamon, nutmeg, and salt. Stir this mixture along with vanilla extract into the sautéed apples and cook until thickened.

In a medium bowl, combine gluten-free flour, brown sugar, chopped pecans, cinnamon, and salt for the pecan streusel. Mix in the cold butter until the mixture resembles coarse crumbs.

Preheat your oven to 350°F (175°C). Poke the chilled crust with a fork and sprinkle with gluten-free flour and granulated sugar.

Spread the apple filling onto the crust and drizzle caramel sauce over it.

Distribute the chilled pecan streusel over the filling.

Bake the tart for 15 minutes, then increase temperature to 375°F (190°C) and bake for an additional 5-10 minutes until golden brown.

Reduce the oven temperature back to 350°F (175°C) and bake for 32-38 minutes more, or until the filling is bubbling.

Allow the tart to cool slightly before serving.