I've been cooking for about 4 years and definitely still have a lot to learn. My favorite cookbook is "Kitchen Sense" by Mitchell Davis. For those who don't know it, I'd say it's similar to "How to Cook Everything", but has fewer recipes (especially basic recipes). At one point I decided I would try to cook every recipe in it, to force me to learn some that I would naturally avoid. (For instance, I'm intimidated by shellfish beyond shrimp and scallops. There are probably also some ingredients/techniques I avoid without even realizing it.) After cooking from it a lot (by my standards) for a few months, I had barely scratched the surface.
I'm interested in another (shorter) cookbook to try this with. Maybe 50 recipes or so. I prefer an general-purpose cookbook, not from a particular cuisine. I also want to steer away from books whose main point is simplicity, like "Rachel Ray 30 Minute Mains". (If these are too many restraints, then a book that restricts to vegetarian recipes, or salads, would be okay.) So far, Cook's Illustrated magazines are the best I've come up with. I think they're not optimal though because I would just be randomly choosing some particular issues.
If this seems like a ridiculous aim, here's an analogy I have in mind. A very thorough and impressive way to learn the material in a math textbook is by doing all of the exercises. I was thinking about this and wondering what the cooking equivalent would be, and this is what I came up with. If you can think of a closer equivalent, suggest that instead!