"The Wise Encyclopedia of Cookery". More of a dictionary or reference book than recipe book (although it has plenty of those), it will tell you more about everything than you can ever need to know. I have shelves full of cookbooks, but the recipes I use most often are actually on cards or clipped from magazines/newspapers. Or copied from murder mysteries.
(If you like that genre, read books by Diane Mott Davidson - her main character is a caterer with "killer" recipes!
) Plus I have my Mom's and Great-Aunt's books and notes...dating back to the 1930s. Don't use the lard anymore...
Although I use cookbooks for the recipes I am most often found reading them like novels!