In a 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 in the egg and mix until a smooth dough forms. Shape the dough into a disk, wrap in plastic, and chill in the fridge for at least 1 hour.

Peel and dice the apples into bite-sized pieces. Transfer to a large bowl and add lemon juice, tossing gently to coat. Set aside.

In a medium saucepan over medium heat, melt unsalted butter. Add diced apples and cook for 3 to 5 minutes until they soften slightly. Stir in brown sugar, cornstarch, cinnamon, nutmeg, and salt until apples are coated and mixture thickens.

Mix gluten-free flour, brown sugar, chopped pecans, cinnamon, and salt. Add cold, cubed unsalted butter and mix until crumbly. Refrigerate.

Preheat your oven to 350°F (175°C). Roll out the chilled dough and place it into the tart pan. Poke holes in the bottom to prevent bubbling and sprinkle with gluten-free flour and sugar.

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

Bake at 350°F (175°C) for 15 minutes. Remove weights and parchment, increase temperature to 375°F (190°C) and bake for another 5-10 minutes until streusel is golden brown. Reduce back to 350°F and bake until set and aromatic for 32-38 minutes.

Allow to cool for at least 15 minutes, drizzle with caramel sauce before serving. Serve warm.