1/2cup(1 stick) unsalted butter, cut up into cubes
3large egg yolks
Instructions
Whisk the sugar, lemon zest, lemon juice and butter cubes in a small saucepan over medium-low heat.
Once butter is melted, whisk in egg yolks, one at a time, incorporating thoroughly. Whisk constantly until the mixture thickens and bubbles start to come to the surface; about 15 minutes. You must whisk the entire time, or the eggs might curdle and cook separately from the curd.
Once the curd is thick and starting to boil, remove the pan from the heat, and push the curd through a fine mesh sieve into a clean container. Cool to room temperature. Then place curd in the refrigerator until ready to use. Curd will continue to thicken as it cools. Keep refrigerated.
Notes
*If curd boils too soon and doesn't thicken: Mix 2-3 tsp of cornstarch with 2-3 tsp of COLD water or lemon juice. Whisk into boiling curd mixture; will thicken quickly.