Remove the zest of 3 lemons using a vegetable peeler. Do not cut into the white pith!
Squeeze the juice out of the fruit (you'll need 1/2 cup) and set aside.
Add the sugar and zest to the food processor and pulse until the zest is finely minced.
In a medium size bowl, cream the butter.
Add in the sugar and lemon mixture and beat until combined.
Add 1 egg at a time, making sure to fully incorporate it into the mixture before adding the next egg.
Add the lemon juice and salt and mix.
Transfer the mixture to a 2 quart saucepan and cook over low heat until the mixture has thickened (approximately 10 minutes). Make sure to stir constantly to avoid scorching.
Remove the lemon curd for the heat when it hits 170 degrees (right under simmering).
Pour the mixture into a glass jar (we like Mason jars) and refrigerate overnight.