Éclair Paris-Brest

Ingredients

• •1 recipe Choux Pastry (made with milk and water and the optional sugar), transferred to a pastry bag fitted with a 3/4-inch star tip
• •1 large egg
• •1 c. à soupe (15ml) water
• •226 g (8 ounces) unsalted butter, softened to about 68°F (20°C)
• •1 recipe Pastry Cream, at room temperature, about 68°F (20°C)
• •113 g chopped semi-sweet chocolate, 56% cacao (4 ounces; 3/4 cup)
• •60 g unsalted butter (2 ounces; 1/4 cup), cut into 1/2-inch cubes
• •1 c. à soupe (15g) light corn syrup
• •1 /8 teaspoon Diamond Crystal kosher salt; for table salt, use half as much by volume

Method

1. 1.Prepare the Choux: Adjust oven rack to middle position and preheat oven to 425°F (220ºC). Using a pen or pencil, trace an 8-inch circle in the center of a 12- by 16-inch sheet of parchment paper. Flip parchment over so that drawn ring is on underside and set on a large, rimmed baking sheet. Pipe a small amount of choux dough under each corner of parchment paper lining baking sheet (dough acts as a glue and keeps paper in place as you pipe).
2. 2.Holding filled pastry bag at a 90 degree angle, about 1-inch away from parchment paper, apply steady pressure and slowly pipe ring of choux along traced circle. To stop piping, cease applying pressure and swirl pastry tip away from piped ring. Pipe a second ring of choux just inside first ring, making sure that the two rings are touching one another. Pipe a third, final ring of choux on top of, and nestling in the groove between, the two piped rings. To smooth out surface of dough, dip a finger into additional cold water and gently pat down any bumps as needed.
3. 3.In a small bowl, whisk together egg and 1 tablespoon water until smooth. Using a pastry brush, gently brush choux rings with egg wash. Bake in preheated oven until choux is puffed and light golden brown, about 15 minutes. Without opening the oven door, reduce oven temperature to 350°F (175ºC). Bake until deep golden brown, 30 to 35 minutes. Turn off oven, partially open door, and let choux stand in turned-off oven for 30 minutes to allow pastry to dry and fully set. Remove from oven and let cool completely, about 15 minutes.
4. 4.While choux is cooling in oven, prepare the Crème Mousseline: In the bowl of a stand mixer fitted with a paddle attachment, beat butter on medium speed until fluffy and light, about 5 minutes. Using a rubber spatula, scrape down bowl and beater. With mixer on medium speed, add pastry cream a few tablespoons at a time, pausing to scrape down bowl and paddle as needed, until thoroughly incorporated, about 1 minute. Switch to whisk attachment and whip mixture on medium speed until Crème Mousseline is soft and airy, about 3 minutes. Transfer Crème Mousseline to a pastry bag fitted with a 3/4-inch star tip; refrigerate until ready to use.
5. 5.Transfer cooled choux ring to a large cutting board. Using a serrated knife, cut choux ring in half horizontally. Carefully lift top off and place on a wire rack set inside a large, rimmed baking sheet; set aside.
6. 6.Prepare the Chocolate Glaze: Place chocolate, butter, corn syrup, and salt in a medium-size, microwave-safe bowl. Microwave on high power in 15 second increments, stirring after each increment, until chocolate is melted and mixture is completely smooth, about 1 minute total. Gently pour over top choux ring in an even layer. Allow glaze to set, at room temperature, about 45 minutes.
7. 7.Pipe Crème Mousseline in even rosettes about 1 1/2-inch-high onto cut side of bottom half of choux ring, making sure to apply steady pressure while piping. Place glazed top half of choux ring over piped filling. Using a serrated knife, slice into portions, and serve.