- 2 large egg yolks
- 3 tablespoons sugar
- 1½ tablespoons cornstarch, sifted
- Pinch of salt
- 1 cup whole milk
- 3½ ounces bittersweet chocolate, melted
- 1¼ tablespoons unsalted butter, cut into small pieces, at room temperature
- 1½ cups unbleached all-purpose flour
- ⅔ cup plus 2 tablespoons cocoa powder
- ½ cup granulated sugar
- 3 large eggs
- 1 large egg yolk
- ⅔ cup milk
- 3 tablespoons unsalted butter, melted
- 1 tablespoon baking powder
- 1 teaspoon vanilla extract
- 1 teaspoon salt
- About 3 quarts vegetable oil
- ½ cup confectioners’ sugar
For Pastry Cream: In a large bowl, whisk together egg yolks, sugar, cornstarch and salt until thick and pale, about 2 minutes. In a medium saucepan, bring milk to a boil over medium heat; remove from heat.
In a slow and steady stream, whisking constantly, add about 2 tablespoons of the hot milk to the egg mixture; then, whisking, add remaining milk. Pour the mixture back into the saucepan, return to medium heat, and, whisking constantly and vigorously, bring to a boil. Cook, whisking constantly and into the edges of pot, until mixture is thickened, 1 to 2 minutes. Remove from heat, whisk in chocolate, and let sit for 5 minutes. Whisk in butter pieces, one at a time, until pastry cream is smooth and silky. Transfer cream to a clean bowl, immediately cover the surface with plastic wrap to prevent a crust from forming, and chill until cold, about 1 hour (pastry cream can be made up to 1 day ahead).
For puffs: In a bowl, whisk together flour, ⅔ cup cocoa powder, granulated sugar, eggs, egg yolk, milk, butter, baking powder, vanilla and salt until smooth.
Heat about 3 inches oil to 375° in a 3-quart heavy pot over medium-high heat. Drop teaspoonfuls of batter into oil and fry, about 10 at a time, until puffed and dark golden, 1 to 1½ minutes. Using a slotted spoon, transfer puffs to paper towels to drain.
Transfer filling to a large pastry bag fitted with a ¼-inch plain tip. Insert the pastry tip into the center of one puff; pipe in about 1 teaspoon pastry cream (do not overfill). Transfer filled puff to a parchment-lined baking sheet and repeat with remaining puffs.
In a bowl, whisk together remaining 2 tablespoons cocoa powder and confectioners’ sugar; dust puffs with cocoa mixture. Serve at room temperature.