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

While the dough is chilling, peel and dice your apples. Toss the diced apples with fresh lemon juice in a bowl to prevent browning.

In a skillet, melt a tablespoon of butter over medium heat. Add the diced apples and sauté for 3–5 minutes until softened. Stir in the brown sugar, cornstarch, cinnamon, nutmeg, and a pinch of salt. Cook until thickened, about 2 minutes, then set aside to cool.

In another bowl, whisk together the gluten-free flour, brown sugar, chopped pecans, cinnamon, and salt. Cut in the cold butter until crumbly.

Preheat your oven to 350°F (175°C). Roll out the chilled tart dough on a floured surface; transfer it to the tart pan. Prick the bottom with a fork.

Spread the cooled apple filling evenly over the crust. Drizzle caramel sauce over the apples, then top with the pecan streusel mixture.

Bake the tart for 15 minutes. Remove weights if used, increase the temperature to 375°F (190°C), and bake for another 5-10 minutes until golden. Lower the heat to 350°F and bake for 32-38 minutes, until the filling is set.

Remove from the oven and allow to cool for at least 15 minutes. Drizzle with extra caramel before slicing. Serve warm with ice cream or whipped cream.