It's not a difficult sauce, really. Basically it's a butter-lemon sauce, sometimes with the addition of chicken broth, or a water and cornstarch slurry, or a little white wine. I've never seen more than four ingredients called for in the recipe, and sometimes just butter and a few drops of lemon juice.
I think it's interesting that the first page inside the Williams-Sonoma book on Sauces, is a photo of a slice of lemon! A lemon slice is also featured on the dust jacket (cover)!