Whisk together the eggs, egg yolk and sugar in a microwave safe bowl or container. Metal whisks and kitchen tools may affect the final taste of your curd, so use plastic or silicone utensils if possible.
Stir in the melted butter, lemon and lemon zest. I didn't want chunks of zest in my curd, so I cut larger ribbons of zest with a vegetable peeler so that I could easily fish them out later.
Stir in the cornstarch/water mixture until well combined.
Microwave for one minute at a time, stirring after each minute.
Curd is finished when the mixture is able to coat the back of a spoon. Mine took about 4 1/2 minutes.
(Optional) Strain the curd through a fine mesh strainer to get rid of any small bits of cooked egg or unwanted lemon zest.