Instructions

for the pastry cream

  Bring half-and-half, 6 tablespoons sugar, and salt to simmer in medium saucepan over medium-high heat, stirring occasionally.
Meanwhile, whisk egg yolks, cornstarch, and remaining 2 tablespoons sugar together in bowl until smooth. Slowly whisk 1 cup of hot half-and-half mixture into egg mixture to temper, then slowly whisk tempered egg mixture into remaining half-and-half mixture in saucepan. Reduce heat to medium and cook, whisking constantly, until mixture is thickened, smooth, and registers 180 degrees, about 30 seconds. Off heat, whisk in butter, chocolate, and vanilla. Transfer pastry cream to clean bowl and press greased parchment paper on surface. Refrigerate until cold and set, at least 3 hours or up to 2 days.

for the pastry

Adjust oven rack to middle position and heat oven to 400 degrees. Line rimmed baking sheet with parchment paper.
Beat eggs and white in 2-cup liquid measuring cup until well combined. (You should have about 1⁄2 cup egg mixture. Discard excess.) Set aside. Bring water, butter, milk, sugar, and salt to boil in small saucepan over medium heat. Remove from heat and stir in flour until incorporated and mixture clears sides of saucepan. Return saucepan to low heat and cook, stirring constantly using smearing motion, until paste is slightly shiny with wet-sand appearance and tiny beads of fat appear on bottom of saucepan, about 3 minutes (mixture should register 175 to 180 degrees).
Immediately transfer hot paste to food processor and process with feed tube open for 5 seconds to cool slightly. With processor running, gradually add reserved egg mixture in steady stream until incorporated. Scrape down sides of bowl and continue to process until smooth, thick, sticky paste forms, about 30 seconds longer.
Fit pastry bag with 1⁄2-inch plain tip and fill with warm pate a choux. Pipe pate a choux into eight 5 by 1-inch logs spaced about 1 inch apart on prepared sheet. Use your dampened finger or back of wet teaspoon to even out shape and smooth surface of each log.
Bake for 15 minutes (do not open oven door), then reduce oven temperature to 350 degrees and continue to bake until pastries are golden brown and fairly firm (pastries should not be soft and squishy), 8 to 10 minutes longer.
Remove sheet from oven. Using paring knife, cut 3⁄4-inch slit into side of each pastry to release steam. Return pastries to oven, turn off oven, and prop door open with handle of wooden spoon. Dry pastries in turned-off oven until centers are just moist (not wet) and surfaces are crisp, about 45 minutes. Transfer pastries to wire rack and let cool completely, about 30 minutes.

for the glaze

Using tip of paring knife, cut 3 small Xs along top of each pastry. Fit clean pastry bag with 1⁄4-inch plain tip and fill pastry bag with pastry cream. Pipe pastry cream into pastries through each opening until éclairs are completely filled.
Microwave chocolate in bowl at 50 percent power until melted, about 30 seconds. Whisk in half-and-half until smooth. Gradually whisk in sugar until smooth.
Transfer éclairs to wire rack set in rimmed baking sheet. Spoon warm glaze evenly over tops, making sure to cover holes completely. Let glaze set, about 20 minutes, before serving.