In a medium bowl, whisk the eggs until well blended. Combine the sugar, lemon juice, butter, and lemon zest in a small (1- to 2-quart) saucepan. Gently heat over medium-low heat until the butter has melted. Don't let the mixture come to a boil. Remove the pan from the heat and whisk the lemon mixture into the beaten eggs. Pour the mixture back into the saucepan and cook gently over medium-low heat, stirring constantly with the whisk, until the mixture thickens and reaches at least 160°F, about 5 min. Again, don't let the mixture boil.
Let the lemon curd cool briefly before transferring it to a heatproof container. Press a piece of plastic wrap onto the surface of the curd and poke a few holes in it with the tip of a knife—this will keep a skin from forming on the curd. Refrigerate until completely chilled. The curd will continue to thicken as it cools.
Make Ahead Tips
The curd will keep, covered in the refrigerator, for up to a week.
nutrition information (per serving):
per 2 Tbs.;