The Preparation
Whisk egg yolks and sugar together in a saucepan until combined.
Add lemon juice and zest.
Cook over medium-low heat, stirring constantly, until mixture thickens and coats the back of a spoon.
Remove from heat and stir in butter one tablespoon at a time until fully incorporated.
Strain through a fine mesh sieve into a bowl.
Press plastic wrap directly onto the surface to prevent a skin from forming.
Refrigerate until set.
