...at least I think, it is. I stumbled into this article and I was shocked. Ohkay, so I have no right to judge. I haven't even read both of the cookbooks. But still, if several recipes are (almost) identical, don't you begin to wonder? I mean, like putting spinach puree in brownies, that rather sounds insane (at least to me!). But Ms. Lapine and Jessica Seinfeld wrote recipes concerning brownies, with spinach and all that. Plus the fact that Ms. Lapine tried to offer her manuscript to Seinfeld's publisher twice, and got rejected. And it is said that the wordings are similar, even the lay-out. It might be coincidence, yes, but it certainly makes me wonder. (Lapine's book, The Sneaky Chef, was published months before Seinfeld's, btw.)
I have to say that this idea isn't original. Not at all. My mom's been doing it for ages, and IIRC, my grandma did that, too. You know, pureeing veggies or sneaking them into your children's dishes. And I guess you can't really prove whether Seinfeld's plagiarizing Lapine's works or not. However, when Jerry Seinfeld went to the Letterman Show and said those horrible things... I mean, c'mon. It's not funny anymore. I'm quite disappointed with him, tell you the truth, since he's one of the comedians that I love. It just sounds so... crass.