If you want to talk about useful Grimoires, I have one of magical proportions in my posession.
Passed down through two generations, it is a mystical tome of mastery.
The Betty Crocker cook book. That's right. Over three decades old, it can teach even the most useless peon to be a veritable wizard of homecookery. Written in the crude tongue of english, the words within it's bindings are said to contain great power...the power to make stuffed peppers, and boil eggs properly.
Now that truly is magic! Sounds like I could do with a copy... cooking is not my forte.