5 tablespoons unsalted butter at room temperature - cut into 1-tablespoon chunks
Instructions
Fill a saucepan with water several inches deep and place over medium heat; bring to a boil, then reduce to a simmer.
Place eggs into a metal mixing bowl; add sugar and lemon juice. Place the bowl over the saucepan with simmering water and whisk continuously until mixture foams and becomes thick, hot, and smooth, 8 to 10 minutes.
Remove from heat; whisk in lemon zest and unsalted butter. Continue whisking until butter melts and incorporates into lemon curd.
Press plastic wrap onto the curd's surface to prevent skin from forming. Refrigerate until chilled and set, about 1 hour. Stir before serving.