Either works - adding only yolks yields a richer custard I think, but it's my belief that the albumen carries some important quality to the end product - somewh

Either works - adding only yolks yields a richer custard I think, but it's my belief that the albumen carries some important quality to the end product - somewhat mysterious, but anyway I usually use the whole egg. I sometimes throw an additional yolk or three in there if I'm feeling luxurious, exactness is not key to the ratios. If you mix the custard the night before too it develops a lovely flavor profile by morning.