Directions

1. Whisk together flour, granulated sugar, and salt in a large bowl. Add butter, and toss until coated. Smash and rub butter between fingers until butter is in small pieces. Freeze, uncovered, until butter is firm, about 20 minutes. Drizzle ice water over flour-butter mixture; toss and stir until a shaggy dough forms. Knead using hands in bowl until dough forms, 2 to 3 minutes. Place dough on a sheet of plastic wrap; cover with another sheet of plastic wrap, and press into a 6-inch square, about 1-inch thick. Wrap tightly; refrigerate for at least 2 hours or up to 24 hours. Remove dough from refrigerator; unwrap and roll into an 18-inch square on a floured work surface. Fold dough into quarters. Wrap tightly in plastic wrap and refrigerate for 1 hour.
2. Whisk together brown sugar, cinnamon, nutmeg, and 1/8 teaspoon salt in a medium bowl; set aside. Core apples using an apple corer but do not peel; set aside. Line a large rimmed baking sheet using parchment paper; set aside. Whisk together egg, water, and remaining 1/8 teaspoon salt in a small bowl; set egg wash aside.
3. On a well floured work surface, roll Pastry into an about 22 x 15 inches rectangle (about 1/16-inch-thick).. Trim edges into a 21- x 14-inch rectangle; discard scraps. Cut into 6 (7-inch) squares.
4. Working with 1 Pastry square at a time, brush egg wash lightly around border; place 1 cored apple in center of Pastry. Place 1 teaspoon brown sugar mixture in hole of apple. Add 1 teaspoon chopped nuts, and then add 1 teaspoon brown sugar mixture. Top hole with 1 piece of the cold butter. Take 1 corner of Pastry and pull up and over apple so Pastry covers the hole; press Pastry down. Going around apple, pull and tuck each corner of Pastry up and over apple. (There should be 4 "wings" sticking out on each side.) Pinch and seal Pastry using your fingers. Repeat process with remaining 5 apples, 10 teaspoons brown sugar mixture, 5 teaspoons chopped nuts, and 5 pieces cold butter. Place Apple Dumplings on prepared baking sheet; refrigerate, uncovered, until firm, about 1 hour.
5. While dumplings chill, preheat oven to 450°F with rack in lower third position.
6. Brush sides and top of each dumpling with egg wash, and sprinkle all over with turbinado sugar. Bake until light golden brown, about 10 minutes. Reduce oven temperature to 375°F and continue baking until pastry is golden brown all over and a paring knife poked into center of apples meets some resistance, 15 to 20 minutes. (The apples should feel slightly underdone, but will continue cooking, sealed in Pastry, after removed from oven. If you overcook them, you'll have applesauce surrounded by Pastry.) There may be a bit of buttery, sugary, juicy goodness coming out of the bottom.
7. Let dumplings cool for 20 minutes on baking sheet on a wire rack. Serve warm with vanilla ice cream, whipped cream, crème anglaise, and/or warm caramel sauce.