1/2 cup unsalted butter
1 1/4 cups granulated sugar
1 egg yolk
1 cup fresh lemon juice
lemon zest from 3 lemons
Melt butter in microwave, set aside to cool slightly.
Whisk together sugar and eggs in a medium-sized microwave-safe bowl.
Whisk in lemon juice and zest.
Finally whisk in the butter.
Microwave on 50% power for one minute. Stir.
Continue microwaving 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.