In a large mixing bowl, whisk together the flour, granulated sugar, and salt. Add the cold cubed butter. Using a pastry blender or your fingertips, quickly work the butter into the flour until coarse pea-sized crumbs form.

Drizzle in 3 tablespoons of ice water and gently toss with a fork. Add remaining 1 to 2 tablespoons of water one at a time just until the dough comes together into a shaggy ball when pressed. Shape dough into a flat 1-inch thick disk, wrap tightly in plastic wrap, and refrigerate for at least 45 minutes to relax gluten.

Preheat your oven to 400°F (204°C) with an oven rack positioned in the center. Line a large heavy baking sheet with unbleached parchment paper.

In a large bowl, toss the thinly sliced apples with brown sugar, cornstarch, cinnamon, nutmeg, fresh lemon juice, and pure vanilla extract until every slice is evenly glossed.

On a lightly floured surface, roll the chilled dough into a 12-inch circle about 1/8-inch thick. Gently transfer the dough onto the prepared parchment-lined baking sheet.

Arrange the apple slices in neat concentric overlapping circles in the center of the dough, leaving a clear 2-inch border all around. Drizzle any remaining spiced bowl juices over the apples.

Fold the pastry border up and over the outer edges of the apples, pleating the dough gently every 2 inches to form a rustic open-faced crust while leaving the center fruit visible.

Brush the pleated crust lightly with the beaten egg wash and sprinkle generously with coarse turbinado sugar for a crunchy sparkling rim.

Bake at 400°F (204°C) for 35 to 40 minutes, until the crust is deeply golden brown and crisp, and the apples are tender and bubbling gently in the center. Remove from oven and let rest on the baking sheet for 10 minutes.

Generously drizzle warm salted caramel sauce over the warm apples and flaky crust, then sprinkle with flaky sea salt. Slice into wedges and serve warm with a scoop of vanilla bean ice cream.