Ingredients

• 3 cups whole milk
• 8 large egg yolks
• 2/3 cup sugar
• 1/4 cup cornstarch
• 1/4 teaspoon salt
• 1 tablespoon unsalted butter, softened
• 1 teaspoon vanilla
• an instant-read thermometer

Instructions

1. Heat milk in a 2 1/2- to 3-quart heavy saucepan over moderate heat until hot but not boiling.
2. While milk heats, whisk together yolks, sugar, cornstarch, and salt in a heatproof bowl until smooth.
3. Add 1 cup hot milk to yolk mixture in a stream, whisking, then add remaining milk, whisking constantly. Transfer mixture to saucepan and cook over moderately low heat, stirring constantly, until thickened and registers 170°F on thermometer, 6 to 10 minutes (do not boil).
4. Immediately force custard through a fine-mesh sieve into a clean bowl and stir in butter and vanilla. Chill custard, its surface covered with wax paper, until cold and thickened, at least 3 hours.