In a medium-size mixing bowl mix together the sugar and lemon zest until fully combined.
Use a whisk or electric mixer on low speed to cream the butter with the lemon sugar.
Add the whole eggs and yolk one at a time beating well after each addition.
Add the lemon juice. Mix well.
Pour into a heavy bottomed saucepan. Simmer over medium-low heat until thickened to a pudding consistency about 10-12 minutes, stirring constantly to prevent scorching. Adjust the temp down, if needed.
Cool then store chilled in a mason jar or air tight container for up to 1 week.
For a completely smooth lemon curd strain through a fine mesh sieve to remove lemon zest.