This lemon curd is for the Red Currant and Lemon Tartlets recipe.
Combine egg yolks, sugar, lemon juice, and zest in a small saucepan. Whisk to combine. Cook, stirring constantly, for 10 to 12 minutes, until the mixture thickens and coats the back of a wooden spoon. Do not allow the mixture to boil.
Remove saucepan from heat. Add butter, one piece at a time, stirring with the wooden spoon until smooth.
Strain mixture through a fine sieve into a medium bowl. Lay a sheet of plastic wrap directly on the surface of the curd to avoid a skin from forming; wrap tightly. Let cool; refrigerate until firm and chilled, at least 1 hour.
Store lemon curd refrigerated in an airtight container up to 2 days.