Do you use the whole egg in lemon curd or yolks only?

I have a Sunset recipe that uses whole eggs. Really easy and makes fantastic curd.

Both, in a 6:4 ratio, yolks to whole eggs.

It depends on the recipe, for example this amazing lemon cream/curd uses both whole eggs and additional yolks http://food52.com/recipes/16407-tartine-bakery-s-lemon-cream but a curd traditionally uses just the yolks.