In a large mixing bowl, combine gluten-free multipurpose flour, almond flour, and a pinch of kosher salt. Cut in softened unsalted butter and powdered sugar until crumbly. Add egg and mix until a smooth dough forms, wrap it in plastic and chill for at least 1 hour.

Peel and dice the apples into bite-sized pieces. Toss with lemon juice to prevent browning and set aside.

In a saucepan, melt unsalted butter, add apples, and cook for 3-5 minutes until slightly softened. Stir in brown sugar, cornstarch, cinnamon, nutmeg, and a pinch of salt, cooking for an additional minute until thickened.

Mix together gluten-free flour, brown sugar, chopped pecans, and cinnamon in a bowl. Add melted butter to combine into crumbly streusel. Chill.

Preheat oven to 350°F (175°C). Roll out the chilled crust and fit into the tart pan, pricking holes in the bottom.

Spread the apple filling over the crust, drizzle with caramel sauce, and sprinkle streusel on top.

Bake at 350°F for 15 minutes, then increase to 375°F for 5-10 minutes until streusel is golden. Reduce back to 350°F and bake for 32-38 minutes until set.

Let cool for 15 minutes on a wire rack. Drizzle with more caramel if desired before serving.