In the bowl of a stand mixer, combine flour, sugar, and yeast on low speed using the dough hook attachment. Add milk, 5 eggs, and salt, mixing until the dry ingredients become moistened. Increase mixer speed and beat until the dough comes together. Slowly add butter, and continue mixing until the dough detaches from the side and bottom of the bowl. Transfer the dough to a separate bowl and cover tightly with plastic wrap. Allow the dough to rest in a warm place until it almost doubles in size, about 1 1/2 hours.
Gently deflate the dough; press a piece of plastic wrap against its surface to prevent a skin from forming, and refrigerate for 6 hours. After refrigeration is complete, using a rolling pin, roll out the dough to 1/4-inch thickness. Cut the dough into an 8-inch diameter, and place on a baking sheet. Cover with plastic wrap and allow the dough to rise in a warm place.
Preheat oven to 375 degrees F.
Remove the plastic wrap from the risen dough and gently apply a coat of egg wash. Sprinkle some rock sugar over the top. Place on a baking sheet and bake for approximately 12 to 15 minutes, or until the dough is puffed and golden. Transfer the dough to a cooling rack and let cool to room temperature.
In a small saucepan, bring milk and vanilla bean to a gentle boil over medium heat.
In a mixing bowl, whisk together the yolks, sugar, and cornstarch. Whisking all the while, very slowly drizzle a quarter of the hot milk into the yolks. Still whisking, pour the yolk mixture into the saucepan, and over high heat, whisk vigorously without stopping and bring to a boil. Boil for about 1 to 2 minutes, and then transfer to a large bowl. Keep stirring until the mixture reaches 100 to 120 degrees F, or slightly warmer than room temperature. Add softened butter, orange water, and kirsch. When completely combined, gently fold in whipped cream.
Cut brioche in half horizontally. Smooth cream mixture over bottom layer, and place second layer gently on top. Serve.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.
Recipe courtesy of Jean-Claude Perennou, Waldorf-Astoria Hotel, New York, NY