In a small bowl, dissolve the cornstarch in the water. Set aside.
In a saucepan set over medium heat, whisk the lemon juice and sugar together until the sugar is completely dissolved (the mixture doesn’t need to boil.) Remove from the heat and let cool until warm. In a small bowl, whisk the eggs together, and gradually pour into the lemon-sugar syrup, whisking constantly to incorporate. Place the saucepan back over medium heat. Add the cornstarch mixture and whisk to incorporate.
Continue whisking until the mixture is thick like a soft pudding (make sure to whisk constantly so the mixture doesn’t stick to the bottom of the pan and burn.) Remove from the heat. Whisk in the regular heavy cream. If you're expecting a brighter yellow hue, feel free to add a drop of yellow food coloring, but I prefer my lemon curd to retain its natural soft yellow shade.
STORAGE: Transfer to an airtight jar and refrigerate until completely cold. The lemon curd will keep for up to a week.