EATING MY EMPIRE
In a medium saucepan, whisk egg yolks, lemon zest and juice, and sugar. Cook over medium heat, stirring with a wooden spoon, until mixture is thick enough to coat spoon, about 8 minutes. Remove from heat. Add butter, one piece at a time, stirring until smooth.
Pass mixture through a fine sieve into a bowl. Cover with plastic wrap; press directly on surface to prevent a skin from forming. Let cool before serving.