Melt butter in microwave, set aside to cool slightly.
½ cup unsalted butter
Whisk together sugar and eggs in a medium-sized microwave-safe bowl.
1 ¼ cups granulated sugar, 3 large eggs, 1 egg yolk
Whisk in lemon juice and zest.
1 cup fresh lemon juice, lemon zest
Finally whisk in the butter.
½ cup unsalted butter
Microwave on 50% power for one minute. Stir.
Continue microwaving at 100% power in one minute intervals, stirring after each interval until the mixture is thick enough to coat the back of a spoon. (The curd will thicken as it cools.)
Strain curd through a fine-mesh sieve to remove zest.
Pour curd into sterile jars and store for up to three weeks in the refrigerator.