Place the lemons, sugar, and eggs in a food processor and process for a few minutes, until well pureed.

Strain the mixture into a saucepan, pressing to extract as much liquid as possible.

Discard the solids, rinse the strainer and set it over a clean bowl near the stove.

Gently heat the lemon mixture over low heat, stirring constantly, until the mixture begins to thicken.

Immediately strain the curd to stop the cooking.

Add the butter and stir to combine.

Cover and refrigerate until ready to use. This curd will keep in the refrigerator for up to 1 week.