Make the Pastry Dough: In a food processor or large mixing bowl, combine flour, sugar, and salt. Add cold cubed butter and pulse or cut with a pastry blender until butter resembles pea-sized crumbles. Drizzle in ice water 1 tablespoon at a time until dough just begins to clump together. Turn out onto plastic wrap, shape into a flat disk, and chill in refrigerator for 30 minutes.

Prepare the Spiced Apples: In a large bowl, toss the thinly sliced apples with lemon juice, brown sugar, flour (or cornstarch), ground cinnamon, nutmeg, and vanilla extract until every slice is glossy and evenly coated.

Roll Out the Dough: Preheat oven to 400°F (200°C) with an oven rack in the center position. Line a large rimmed baking sheet with parchment paper. On a lightly floured surface, roll chilled dough disk into an approximate 12-inch rustic circle (about ⅛-inch thick). Transfer onto the parchment paper.

Chefs Secret Arrangement Trick: Arrange the spiced apple slices in concentric circles or fan patterns in the center of the dough, leaving a clear 2-inch border around the entire edge. Dot the exposed apples with the 1 tablespoon of butter cubes.

Fold and Pleat: Gently fold the 2-inch border of dough up and over the outer ring of apples, pleating the pastry as you move around the circle. The center of the apples should remain exposed.

Egg Wash and Sugar: Brush the folded pastry crust with beaten egg wash. Generously sprinkle the crust and apples with coarse sparkling turbinado sugar for bakery-style crunch.

Bake to Golden Perfection: Bake for 30 to 35 minutes until the crust is deeply golden brown, audibly crisp, and the apple juices bubble warmly in the center. Allow to cool on the baking sheet for 10 minutes, then slice warm and top with vanilla bean ice cream!