In a medium size sauce pan combine sugar, eggs, lemon zest and lemon juice. Mix until smooth.
Stir over medium heat for about 5 minutes until it comes to a boil. It will thicken up some but will continue to thicken as it cools. Stir constantly.
Cover and refrigerator until it thickens.
Place butter, cut into pieces in a large bowl.
Pour hot liquid through a fine mesh strainer over the bowl. Stir until butter melts.
Keep lemon curd stored in an airtight container in the refrigerator.
Video
Notes
Always use real fresh lemon juice and zest. Do not use that lemon juice that comes in the container at the grocery store. I use regular lemons that you find in the grocery store but it can also be made with Meyer lemons if you have access to them.
When working with lemons, there are a few tools that I find really helpful. A lemon juicer for juicing and a microplaner for zesting.
You can also make curd with any of your favorite citrus juices such as oranges, limes, or grapefruits.