In glass bowl, mix together egg yolks, whole eggs, lemon zest, lemon juice and sugar.
Cook mixture over a double boiler until mixture thickens and coats back of spatula.
Remove from heat, add butter in small ¼ inch pads.
When pads have melted completely, strain mixture through a sieve.
Discard zest, egg and other remnants from sieve.
Store lemon curd in air tight container for up to one week.
