How to Make It
Whisk together milk, yeast, and 1 tablespoon of the sugar in the bowl of a heavy-duty electric stand mixer fitted with a dough hook. Let stand 5 minutes. Add all-purpose flour, bread flour, eggs, 1 teaspoon of the salt, and remaining 3 tablespoons sugar. Beat on low speed until combined, 2 to 3 minutes, stopping to scrape down bowl as necessary. Continue to beat on low speed until dough is loose and sticky, 3 to 4 minutes. With mixer running on low speed, add 1 cup of the softened butter, 2 tablespoons at a time, beating just until blended after each addition. Stop mixer occasionally to scrape down bowl. Increase speed to medium, and beat until dough is sticky and soft, 15 more minutes. (Dough will be glossy, shiny, and elastic.) Increase speed to medium-high, and beat until dough has formed a ball and comes away from bowl cleanly, about 1 more minute. Place dough in a large bowl coated with cooking spray. Loosely cover with plastic wrap, and let rise in a warm place (80°F to 85°F), free from drafts, until doubled in size, 1 1/2 to 2 hours.
Melt 3/4 cup of the butter in a medium skillet over medium. Stir in 2 cups of the brown sugar, and cook, stirring constantly, until sugar melts, 4 to 5 minutes. Remove from heat, and stir in honey, cream, tap water, and remaining 1/4 teaspoon salt. Set aside.
Place remaining 2 1/2 cups brown sugar in a medium bowl. Stir in cinnamon and nutmeg until combined.
Place remaining 1/2 cup softened butter in a microwave-safe bowl, and microwave on HIGH until melted, 20 to 30 seconds. Very gently divide dough in half, and place 1 half on a floured surface. Wrap remaining dough half with plastic wrap, and chill until ready to use.
Roll dough on floured surface into a 16- x 12-inch rectangle with 1 long side facing you. Brush dough with half of the melted butter. Sprinkle with half of the brown sugar-cinnamon mixture, and lightly press to adhere. Starting at long edge farthest from you, roll firmly, jelly-roll fashion, into a log. Using a sharp knife, cut into 16 (1-inch) rounds.
Place 2 rounds, cut side up and with edges touching, on lightly floured surface. Press rounds into a 4- x 5 1/2-inch rectangle with 1 long side facing you. Repeat with remaining 14 rounds, to create 7 more rectangles. Dot 1 tablespoon of the chocolate-hazelnut spread evenly over each rectangle. Sprinkle each with 1 tablespoon of the hazelnuts. Starting at long side farthest from you, roll each rectangle firmly, jelly-roll fashion, into a log. Using a sharp knife, cut 1 log in half lengthwise. With cut edges up, twist pieces together, forming a 5 1/2-inch-long twisted braid. Wrap braid around itself, tucking loose ends under. Repeat with remaining logs.
Repeat Steps 5 and 6 with remaining melted butter, dough half, brown sugar-cinnamon mixture, chocolate-hazelnut spread, and hazelnuts.
Divide cooled brown sugar-butter mixture between 2 (9- x13-inch) baking dishes. Sprinkle evenly with remaining 3/4 cup hazelnuts. Place 8 braided rounds, about 3/4 inch apart, in each prepared dish.
Cover baking dishes with plastic wrap, and chill 6 hours or overnight. Remove from refrigerator, and let stand at room temperature until dough is very puffy and buns are touching, 1 to 2 hours.
Preheat oven to 350°F with 1 rack in upper third and 1 rack in lower third of oven. Place an ovenproof skillet on bottom rack. (Do not remove skillet while oven preheats.) Add hot water to preheated skillet on bottom oven rack. Remove and discard plastic wrap from buns. Place baking dishes on rack above skillet. Bake buns until tops begin to brown, 25 to 30 minutes. Cool in baking dishes on wire racks 10 minutes before serving.