Lemon Pie Filling

In a medium saucepan, combine the sugar, cornstarch, and salt. Gradually stir in the water until smooth.

Cook over medium heat, stirring constantly, until the mixture thickens and begins to boil. Continue cooking for 1 minute.

Remove from heat. Gradually whisk about 1 cup of the hot mixture into the egg yolks, then return everything to the saucepan.

Bring to a gentle boil and cook for 2 more minutes while constantly stirring.

Remove from heat and stir in the lemon juice, lemon zest, and butter until smooth.

Cool slightly before using as a pie filling, or refrigerate until ready to use.