Vitamix® method
Place the eggs and lemon zest in the blender.
Add the lemon juice, sugar and kosher salt. Begin blending on low speed then slowly increase to high and process for about5 to 6 minutes. (The heat produced by the Vitamix®, which is considered a highspeed blender, “cooks” the egg yolks.)
With the machine on low speed add the butter and blend an additional 30 to 45 seconds.
Transfer to a heatproof dish and cover the top with food wrap, placing the wrap directly on the curd to prevent a film to form. Chill until ready to serve.
Stovetop method
In a heavy saucepan add the beaten eggs, sugar, lemon juice and kosher salt, whisking to combine. Cook over medium heat, stirring frequently until the mixture thickens and coats the back of a spoon, about 12 to 15 minutes.
Add the butter and the lemon zest, stirring until the butter has melted and is mixed evenly into the lemon curd. (Add the lemon zest at the end, after cooking the curd or the zest will “candy” during the cooking process. It won’t hurt anything, but it will have a different texture.)
Transfer to a heatproof dish and cover the top with food wrap, placing the wrap directly on the curd to prevent a film to form. Chill until ready to serve.