1Place a saucepan containing several inches of water over medium heat and bring water to a simmer.
2Place eggs into a metal mixing bowl and add sugar and lemon juice. Place bowl over pan containing simmering water and whisk continuously until mixture foams and becomes thick, hot, and smooth, 8 to 10 minutes.
3Remove from the heat; whisk in lemon zest and unsalted butter. Continue whisking constantly until butter melts and incorporates into the lemon curd. Cover bowl with plastic wrap, pushing the plastic wrap onto the surface of the lemon curd. Refrigerate until chilled and lemon curd has set up, at least 1 hour. Stir before serving.
3 large eggs
3/4 cup white sugar
2/3 cup freshly squeezed lemon juice
1 1/2 tablespoons freshly grated lemon zest
5 tablespoons unsalted butter at room temperature - cut into 1-tablespoon chunks