Whisk sugar, butter and lemon zest
Add whole eggs and egg yolk whisk to combine then mix in lemon juice and pinch of salt. Now don't freak out...it will look awful at this point. But it gets better. Trust me.
Add mixture to sauce pan and over low heat begin to cook stirring constantly.
Its starts to look pretty good, as you can see I don't worry about the lemon seeds we are going to strain them out later.
Cook until it starts to thicken, do not let it boil. Check for nappe, it will coat the back of a spoon and when you make a stripe it will stay there.
If you want another way to test for doneness you can use your thermometer, you are looking for a temperature of 170 degrees
Strain. Capturing any lemon seeds, or yucky egg bits.
Place over an ice bath to cool, then place plastic wrap directly on top of the curd and place in the fridge to continue cooling for at least 2-3 hours.