Make Pastry Dough: In a large bowl or food processor, whisk flour, sugar, and salt. Add cold cubed butter. Use a pastry cutter or pulse until butter forms pea-sized crumbs with some larger flaky flakes. Drizzle in ice water 1 tablespoon at a time, tossing gently with a fork until dough just holds together when squeezed. Shape into a smooth flat disc, wrap in plastic, and chill in refrigerator for at least 45 minutes.

Toss Apple Filling: In a medium bowl, gently combine thinly sliced Honeycrisp and Granny Smith apples with lemon juice, brown sugar, cinnamon, nutmeg, and cornstarch. Toss gently until apples are glistening and evenly coated.

Roll Pastry: Preheat oven to 400°F (205°C) and line a heavy rimmed baking sheet with parchment paper. On a lightly floured surface, roll chilled dough disc into an approximate 12-inch circle about 1/8-inch thick. Gently transfer rolled dough onto the parchment paper.

Arrange & Pleat: Arrange spiced apple slices in tight concentric circles starting from the center, leaving a 2-inch border of bare dough around the perimeter. Drizzle 2 tablespoons of warm salted caramel sauce directly over the apples. Fold the dough edges up and over the outer ring of apples, overlapping and pleating rustic folds every 2 inches.

Egg Wash & Sugar: Brush folded pastry borders generously with egg wash, then scatter coarse turbinado sugar lavishly over the crust for irresistible crunch.

Bake to Golden Perfection: Bake at 400°F (205°C) for 35 to 40 minutes, until pastry crust is deeply golden-brown and crisp, and apple juices in the center are bubbling thickly. If crust edges brown too quickly after 25 minutes, tent loosely with foil.

Caramel Drizzle & Serve: Cool on baking sheet for 15 minutes. Drizzle generously with remaining warm salted caramel sauce and sprinkle flaky sea salt. Slice into warm wedges and serve with scoops of melting vanilla bean ice cream!