Rich Custard

Directions

1. 1
   Whisk together 1/4 cup sugar, cornstarch, and a pinch of salt in a 2-quart heavy saucepan.
2. 2
   Whisk in 1/4 cup milk until smooth, then stir in remaining milk and zest.
3. 3
   Bring to a boil over moderate heat, whisking frequently.
4. 4
   Have ready a bowl filled with ice and cold water.
5. 5
   Whisk together yolks and remaining 1/2 cup sugar in a large bowl.
6. 6
   Gradually whisk in hot milk mixture, then transfer custard to saucepan.
7. 7
   Cook, stirring constantly, until mixture registers 170F on an instant-read thermometer, 3 to 4 minutes.
8. 8
   (Do not boil.)
9. 9
   Immediately pour custard through a fine sieve into a metal bowl set in ice water.
10. 10
    Stir in vanilla.
11. 11
    Cool, stirring frequently.