Prepare Lemon Curd, first. If possible, prepare it the night before, or up to a week before you are ready to use it.
Set a food-strainer or a mesh sieve over a medium-sized bowl; set aside.
Pour water into a saucepan; you will need enough water to cover the bottom of the saucepan and come 1-inch up the sides; bring water to a simmer.
Place a heat-resistant bowl over the saucepan.
Add eggs, sugar, and lemon juice to the bowl; whisk until blended.
Continue to cook and whisk constantly until the mixture thickens; about 8 to 10 minutes.
Remove from heat and pour the mixture through previously prepared strainer so to remove any lumps.
Whisk butter into the mixture.
Add the lemon zest and whisk to combine.
Cover with plastic wrap; this will prevent skin formation on top of lemon curd.
Let slightly cool.
Refrigerate for 4 hours, or until thickened and cold.