Favorite? Probably not, but if I had to limit it to one cookbook, I'd use The Best Recipe. It's a 1000 page tome with most everything you want to know how to cook. The reason I love the book though, is their approach. For each recipe, they gather a bunch of different recipes and then make them all, figure out what they like and don't, change the recipes, make them again, etc. until they find the "best" recipe. The fascinating thing about the book is that they document all this along with the recipe, so you can figure out not just how to make a dish, but why you're doing it a certain way. That knowledge, gleaned mostly from this book, is what allowed me to step beyond following a recipe and actually start to cook and be creative in the kitchen.
Also, I would NOT get The French Laundry book. That is not a Tuesday night, throw something together kind of a book. If you want a Keller book, get Ad Hoc at Home. It is by far his most accessible book. But even that wouldn't qualify as a bible for your kitchen. Note: I'm not saying The French Laundry book isn't good, just that it doesn't meet the standard of the question.