The Thrifty Kitchen - written by the daughter and granddaughter of Margaret Fulton. Not just good, thrifty recipes, but some good basic tips on food storage, how to shop, how to season a cast iron pan etc

Catering/professional cookery books are brilliant. With sauces they will give the basic one, then what you do to vary it. Of course there is also the scaling if you happen to be cooking for 100+