In a microwave safe bowl, use an electric mixer to beat sugar and butter until well combined. Continue beating and add eggs, one at a time, until completely incorporated.
Meanwhile, whisk cornstarch into ΒΌ cup lemon juice in a small bowl.
Continue beating sugar mixture and slowly pour in lemon juice, lemon juice/cornstarch mixture, and zest.
Microwave on high for 8 minutes, stopping to stir after 4 minutes. Microwave for an additional 2 minutes, stopping to stir after 1 minute.
Pour through a fine mesh strainer, if desired, to remove any tiny bits of zest or cooked egg.
To prevent a film from forming on the top of the curd as it cools, either place plastic wrap into the top of the mixture or stir regularly during the cooling process. Store in the refrigerator.