In a medium saucepan, combine 5 egg yolks, 1 cup sugar, ⅓ cup lemon juice, lemon zest and ½ cup butter.
Cook over medium heat, constantly stirring until the mixture is thick enough (it usually takes me 10 minutes to get the consistency I want).
Remove from heat and carefully transfer the hot mixture into a heat-proof container. Use a strainer when transferring so you end up with smooth, silky, pure lemon curd.
Cover by putting a layer of plastic wrap directly on the surface of the curd and refrigerate overnight.
Video
Notes
I usually use 2-4 Meyer lemons, depends on the size.