Marcella Hazan's tomato sauce with butter and onion has changed my life. If I were to buy just one of her cookbooks, which one should it be?
I'd go with The Essentials of Classic Italian Cooking (a compendium of her first two books).
I have her first book, Classic Italian Cookbook, which I think is out of print. I love it dearly. I agree with sfmiller. If I was buying one now, I would buy Essentials. Here is a blog of nine women who went through Essentials and cooked every recipe. Marcella commented several times in the blog.
I think I posted the link to the book by mistake. Here's the blog.
I confess that I only own the first two, but if you cook you certainly want those.