For the pastry cream:
2 cups half-and-half
½ cup sugar
5 large egg yolks
3 tbsp. cornstarch
4 tbsp. cold unsalted butter, cut into 4 pieces
1½ tsp. vanilla extract
For the pâte à choux:
2 large eggs plus 1 large egg white
5 tbsp. unsalted butter, cut into 10 pieces
2 tbsp. whole milk
6 tbsp. water
1½ tsp. sugar
¼ tsp. salt
½ cup (2½ oz.) all-purpose flour
For the chocolate glaze:
3 tbsp. half-and-half
2 oz. semisweet or bittersweet chocolate, finely chopped
1 cup (4 oz.) confectioners’ sugar, sifted
To make the pastry cream, heat the half-and-half, 6 tablespoons of the sugar, and the salt in a saucepan over medium-high heat until simmering, stirring occasionally to dissolve the sugar. Meanwhile, combine the egg yolks and remaining 2 tablespoons sugar in a medium bowl and whisk until the sugar has begun to dissolve and the mixture is creamy, about 15 seconds. Whisk in the cornstarch until combined and the mixture is pale yellow and thick, about 30 seconds.
When the half-and-half mixture has reached a simmer, slowly add it to the egg yolk mixture to temper, whisking constantly. Return the mixture to the saucepan, scraping the bowl with a rubber spatula. Return the mixture to a simmer over medium heat, whisking constantly, until a few bubbles burst on the surface and the mixture is thickened and glossy, about 30 seconds. Off the heat, whisk in the butter and vanilla. Strain the pastry cream through a fine mesh sieve set over a medium bowl. Press plastic wrap directly on the surface to prevent a skin from forming and refrigerate until cold and set, at least 3 hours and up to 2 days.
To make the pâte à choux, whisk the eggs and egg white in a liquid measuring cup. You should have ½ cup (discard the excess). Set aside. Combine the butter, milk, water, sugar and salt in a small saucepan. Heat over medium heat and bring to a boil, stirring once or twice. When it reaches a full boil and the butter is fully melted, remove from the heat and stir in the flour until incorporated and the mixture clears the sides of the pan. Return the saucepan to low heat and cook, stirring constantly, using a smearing motion, until the mixture is slightly shiny, looks like wet sand and tiny beads of fat appear on the bottom of the pan (the mixture should register 175-180˚ F on an instant-read thermometer.
Immediately transfer the mixture to a food processor and process with the feed tube open to cool slightly, 10 seconds. With the machine running, gradually add the reserved eggs in a steady stream. When they have been added, scrape down the sides of the bowl, then process 30 seconds more until a smooth, thick, sticky paste forms.
Place an oven rack in the middle position and preheat the oven to 425˚ F. Line a baking sheet with parchment paper. Fill a pastry bag fitted with a ½-inch plain tip with the pâte à choux. Pipe the paste into 1½-inch mounds on the prepared baking sheet, spacing them about 1 to 1¼ inches apart (you should be able to fit 24 mounds on the baking sheet). Use the back of a teaspoon dipped in water to even out the shape and smooth the surface of the piped mounds.
Bake for 15 minutes (do not open the oven door during baking). Reduce the oven temperature to 375˚ F and continue to bake until golden brown and fairly firm, 8-10 minutes longer. Remove the baking sheet from the oven. Use a paring knife, cut a ¾-inch slit into the side of each puff to release steam; return the puffs to the oven, turn the oven off, and prop open the oven door with the handle of a wooden spoon. Dry the puffs in the turned-off oven until the centers are just moist (not wet) and the puffs are crisp, about 45 minutes. Use a sharp paring knife to poke a hole through the bottom or side to check the interior. Transfer the puffs to a wire rack to cool completely. (At this point the puffs can be stored at room temperature for up to 24 hours or frozen for up to 1 month in an airtight plastic bag. Before serving, crisp in the oven at 300˚ F – 5-8 minutes for room temperature puffs, 8-10 minutes for frozen puffs.)
To fill the puffs, use the tip of a paring knife to make a small cut perpendicular to the first, creating an X in the side of each puff. Fill a pastry bag fitted with a ¼-inch plain tip with the pastry cream. Pipe some of the pastry cream through the X into the side of each puff until it starts to ooze back out. Repeat to fill all the puffs.
To make the glaze, place the half-and-half and chocolate in a medium microwave-safe bowl, cover with plastic wrap, and microwave for 20 seconds at a time, until the mixture just begins to steam. Whisk together thoroughly, add the confectioners’ sugar, and whisk until completely smooth. Dip the tops of the filled cream puffs in the chocolate glaze and transfer to a wire rack until the glaze has set completely. Serve within several hours.