Lemon Curd

Have ready a fine-mesh strainer suspended over a medium bowl containing the lemon zest.

In a medium heavy saucepan, whisk the yolks, sugar, and butter until well blended. Whisk in the lemon juice and salt. Cook over medium-low heat, stirring constantly with a silicone spatula (be sure to scrape the sides of the pan), until thickened and resembling hollandaise sauce, which thickly coats