When Martha Stewart first published this recipe in her Martha Stewart Living Magazine in 1995, she had an entire article explaining the "where's/how's/and what not to do's" with regards to lemon curd. I had only ever purchased lemon curd prior to this recipe, and wasn't impressed with it. Too thick, too tart and short shelf life for the very high price. THIS recipe changed my mind: soft, teasingly tart, the ability to make it tarter or softer in flavour all had me saying "THIS IS THE WORLD'S BEST LEMON CURD!!!" I've never tried another recipe since, even Martha's "New & Improved" curd recipes, where she seems to have forgotten what she taught us fans of hers, so many years ago.
According to the article, the reasons why THIS curd recipe is so superior is the following:1) Beating the egg yolks until rich yellow and then straining the first time creates a smooth, albumen-free base. 2) Cooking the mixture WITHOUT the zest creates a "softer", less bitter curd. Cooked zest just becomes more bitter, even without the white pith. 3) A second straining removes any possibility of "scrambled eggs" from your curd! 4) Adding the chilled butter, cut into pieces, to the eggs does two things: it rapidly cools down the curd so it doesn't continue to cook and also the buttery flavour is not changed by cooking with the yolks! 5) Adding the zest after the curd is cooled creates a smooth, flavourful but not bitter curd!
Are these steps too many for some people? Oh, I'm sure of it, especially the straining steps. And some curd recipes have you dump everything together in the pan so that sure makes it simple. However, after 15 years of making this one curd recipe, I've found the little bit of extra time involved in creating it makes for a superiour end product.
NOTE: If you do not want a dense, eggy Lemon Curd, use WHOLE EGGS for the recipe, rather than egg yolks. That would be four whole eggs to the six egg yolks.