Ingredients

　　6 large egg yolks

　　1 tablespoon finely grated lemon zest plus 1/2 cup fresh lemon juice (from 3 lemons)

　　3/4 cup sugar

　　Pinch of salt

　　1/2 cup (1 stick) cold unsalted butter, cut into pieces

　　Whisk together yolks, zest, juice, sugar, and salt in a heavy saucepan. Bring to a simmer over medium heat, whisking constantly. Cook until thickened, 8 to 10 minutes. Strain through a fine sieve into a bowl. Whisk in butter, one piece at a time, until smooth. Press plastic wrap directly onto surface, and refrigerate until cold, 1 hour or up to 1 day.

　　Martha Stewart's New Pies and Tarts