Measure out 1/4 cup lemon zest and 1/3 cup lemon juice. Slice butter into 1 tablespoon chunks and keep in refrigerator. Prepare all ingredients.

In a double boiler, whisk together egg yolks and sugar over boiling water until smooth.

Add lemon juice and zest to the egg mixture. Continue whisking for about 8-9 minutes until mixture begins to thicken.

Remove from heat. Gradually whisk in butter, one tablespoon at a time, until smooth. Pour into a bowl, cover, and refrigerate for about 2 hours until thickened and cooled.