Is there a single source for the basics of cooking (sauces, herbs, oil usage, etc)? I'm a decent cook but I know that there are huge gaps in my knowledge of the fundamentals of cooking.  I assume that aspiring chefs learn a great deal of this in culinary school but I was hoping that there might be a book or resource for explaining not only the "hows" of making things like a good mayonnaise but also the "whys". 

So is there a book or cookbook thats considered best in class for the basics of cooking?
I find that anything Cooks Illustrated puts out usually has a decent list of "whys" and have been garnering them up over the years.  Unfortunately this can leave you something of a specialist with deep knowledge on whatever their articles cover, but if you want to learn the why of something, they are a great source.

For baking in particular Ratio is an excellent book.