I have a question about the ingredient "quarters preserved lemon, rinsed". What is a preserved Lemon?
Preserved lemons are akin to pickled lemons, they are salted and cured for a certain amount of time. Making them edible/palatable and great in a multitude of dishes.
You can easily make them yourself--although they take several weeks until they are ready. Or you can buy them in jars at a Middle Eastern grocery shop. Whole Foods used to sell them individually (one lemon goes a long way). They have not had them for several months now, but tell me they should have them in stock sometime in March.
There are several very good recipes for the lemons on the site, and one in a Hotline answer, from Pegeen:
There is a quick version from Mark Bittman you could try (check the comments in that question).
I use home-made preserved lemons, quite well aged, rinsed but with both peel and pulp (watch for seeds). This really gives the hummus a punch.