- 4 large egg yolks
- 1/4 cup sugar
- 3 tablespoons cornstarch
- 3 tablespoons unsweetened cocoa powder
- 1/4 teaspoon salt
- 1 cup milk
- a 3-ounce bar fine-quality bittersweet chocolate (not unsweetened), broken into pieces
- 2 tablespoons unsalted butter, cut into bits and softened
- In a heatproof bowl whisk together yolks, sugar, cornstarch, cocoa powder, and salt (mixture will be very stiff). In a heavy saucepan bring milk just to a boil over moderate heat and in a stream add 1/4 cup to egg mixture, whisking until smooth, and whisk in remaining 3/4 cup milk. Transfer egg mixture to pan and bring to a boil, whisking (mixture will look curdled but will become smooth as whisked). Boil pastry cream, whisking vigorously, 1 minute and remove from heat. Stir in chocolate and butter, stirring until melted and combined well. Transfer hot pastry cream to a heatproof bowl and chill, surface covered with plastic wrap, until cold, about 2 hours. Pastry cream may be made 2 days ahead and chilled, covered.