Zest the lemons, then slice them in half and juice them into a measuring cup. Use a small colander or a lemon juicer to keep out any seeds.
Place the egg yolks, cornstarch, and salt in a large bowl. Whisk well to combine and set aside.
Add your lemon juice, granulated sugar, and lemon zest to a large, shallow sauté pan.
Stir constantly with a whisk and bring to a simmer over medium heat.
When it has reached a simmer, scoop about 1 cup of the lemon juice mixture and slowly add it into the egg yolk mixture while whisking.
Add the tempered egg mixture back into the lemon mixture while whisking constantly.
Whisk constantly and cook over medium heat until desired thickness.
Add your butter in chunks to the lemon curd and whisk until the butter is melted and combined.
Pour the finished lemon curd into a heat-proof jar or bowl. Cover the curd with plastic wrap so that it is touching the surface of the curd without any air bubbles in between.
Store it in the fridge for up to one week or freeze it for up to a year.
