Reddit mentions of Old Mr. Boston Deluxe Official Bartender's Guide

There are also some great reference books on cocktail making. A good place to start, IMO, is with the recently-released (and amazing) Cocktail Codex, which I recently read through and loved. It's, unfortunately, not available from HPL, but buying it would be less than a class would cost, and will give you way more information.

A lot of cocktail books are either just lists of recipes or are built for people with such a massive store of knowledge already. Either of those areas aren't good for people in your position, but this one does a good job of teaching the fundamentals in a way that's easily applicable both with and without recipes.

Don't feel like you have to learn to make everything all at once. Cocktail Codex is split into six sections (the thrust of the book is that almost every cocktail can be thought of as a variation on one of the old-fashioned, martini, daiquiri, sidecar, whisky highball, and flip). Buy a few bottles that can help you do a few things and start from there. You can always add to your collection and branch out later. Then you can slowly end up filling several of your kitchen cabinets with various amari and a surprising/unnecessary number of bottles of Fernet Branca until your spouse is equal parts happy and slightly annoyed.

Some other great reference books that I'd recommend:

• The Joy of Mixology, Revised and Updated Edition
  
• Imbibe (this one's more history than craft, FYI)
  
• Mr Boston (not as much theory, but a bajillion recipes)