Lime Curd

6 large egg yolks
3/4 cup sugar
1/2 cup fresh lime juice
3 tablespoons heavy cream
3/4 stick (6 tablespoons) cold unsalted butter, cut into pieces
2 teaspoons freshly grated lime zest

In a heavy saucepan, whisk together yolks, sugar, lime juice, cream, and butter and cook over moderately low heat, whisking constantly, 5 to 7 minutes, or until mixture just reaches a boil (do NOT allow to boil).  Strain curd through a fine sieve into a bowl and stir in zest.  Cool curd with its surface covered with plastic wrap, and chill at least 4 hours and up to 2 days.