Instructions

1. In a large bowl, beat the butter and sugar together with an electric mixer until
   smooth. In a separate bowl, beat the whole eggs and yolks with a fork until
   fully blended.
   
2. Then, a little at a time, add the beaten eggs to the creamed butter mixture,
   until smooth. Once smooth, mix in the lemon juice and beat for 1 minute on high
   speed.
3. The mixture will look curdled in the mixing bowl because of the flecks of
   butter. It will turn satiny as it cooks.
   
4. Pour the mixture into a medium, heavy, nonreactive saucepan and cook over
   medium heat for 10 to 15 minutes; stirring constantly, until the curd thickens,
   never letting it boil. Test for set by coating the back of a wooden spoon and
   dragging your finger through it. If a distinct track remains, it’s done.
5. Remove from the heat and stir in the lemon zest, and salt.
   
6. Ladle into hot, sterilized jars and store in the refrigerator for up to 3
   weeks.