- Strain the yolks and whole eggs and lemon juice through a sieve into a medium-heavy non-reactive saucepan. Add sugar; whisk to combine.
- Cook over low heat, stirring constantly with a wooden spoon, until the mixture thickens and coats the back of the spoon, about 15 minutes. Remove from heat; stir in the butter, one piece at a time, until fully incorporated. Stir in lemon zest. Place over a bowl of ice to bring to room temperature.
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