Juice the lemons. Remove any seeds that may sneak through. You will need 1 cup of lemon juice.
Add the butter, lemon juice, lemon zest, sugar and salt to a sauce pan over medium to medium low heat. Heat until the butter starts to melt, stirring occasionally.
Add the eggs to a bowl and beat well.
When the butter has melted, gradually add a cup or so of the warm lemon mixture to the eggs while whisking. You need to temper the eggs so you don't end up with scrambled eggs.
Add the egg mixture back to the sauce pan and whisk well.
Continue to cook the the mixture over medium low heat, using a wooden spoon to stir it constantly. Once it comes to a boil, reduce the heat to simmer and continue to cook, up to one hour, until it thickens.
Cool slightly then run the mixture through a strainer. Add the Lemon Curd to jars or containers. I yielded just over 2 pints.
Notes
When grating (or zesting) the lemons, remember to only use the yellow outer skin. The white part of the lemon is very bitter. Store the lemon curd in an air-tight container in the refrigerator for up to two weeks.