Make the Flaky All-Butter Pastry: In a large bowl, whisk flour, sugar, and 1/2 tsp salt. Add cold cubed butter. Use a pastry blender or fingertips to work butter into flour until pea-sized clusters form. Drizzle in ice water 1 tablespoon at a time, mixing gently with a fork until dough just holds together. Shape into a smooth 1-inch thick disc, wrap tightly in plastic, and chill in the refrigerator for at least 45 minutes.

Toss Spiced Apple Filling: In a medium bowl, gently toss sliced Honeycrisp and Granny Smith apples with lemon juice, dark brown sugar, cinnamon, nutmeg, and 1 tablespoon flour until every slice is evenly coated.

Roll the Dough: Preheat oven to 400°F (200°C). Line a large baking sheet with parchment paper. On a lightly floured surface, roll chilled dough out into a rough 12-inch circle (about 1/8-inch thick). Transfer dough onto the parchment-lined baking sheet.

Arrange Apples & Pleat Crust: Arrange apple slices in tight concentric fanned circles or rosettes in the center of the dough, leaving a 2-inch border all around. Gently fold and pleat the dough border up and over the outer edges of the apples, overlapping the folds as you work around the circle.

Egg Wash & Bake: Brush the pleated dough crust generously with the egg wash. Generously sprinkle the crust with coarse turbinado sugar. Bake at 400°F for 35 to 40 minutes until crust is deep golden brown, flaky, and apple juices bubble thick in the center.

Glaze with Salted Caramel & Serve: Remove galette from oven and let cool on pan for 10 minutes. Warm salted caramel sauce and generously drizzle over the caramelized apples and crust. Finish with a pinch of flaky sea salt. Slice warm and serve with a scoop of vanilla bean ice cream.