Add the lemons, salt, sugar, and eggs to bowl of a blender with a high speed setting. Blend, beginning slowly on a low speed. Then move up to variable 10 if a Vitamix blender or similar setting on another type of blender for 10 minutes.

Decrease the blender speed to 3 or 4 and add butter, 1 chunk at a time, until you have added all the butter. Increase blender speed back to 10 and blend for about 10 seconds. The curd should be hot and not very thick. A spoonful of curd should not drip off the bottom of the spoon.

Chill in the refrigerator before serving. When chilling the curd, cover the top with plastic wrap to prevent a skin from forming.

Freezes well if tightly wrapped.