Ratios
I've been doing a bit of digging into the books-on-food portion of my bookshelves lately; like most bachelors I have around 10 feet of shelf space devoted to books of this sort. Lately that's meant reading more closely through Michael Ruhlman's book Ratios: The Simple Codes Behind the Craft of Everyday Cooking
Rather than a typical cookbook, this one is more of a meta-recipe book. i.e. it's not focused on how you make, e.g., a double chocolate-chip cookie as it is on how you can make a generic cookie and how that cookie changes when you adjust particular types of ingredients.
One thing that I think taking cooking classes helped with is my sauce-making, and now I'm trying to both diversify and apply that a bit more. So far this sort of book seems to be helping. Chef at Home also isn't bad, although the semi-faux-realism of most of these shows gets a bit tedious after a while.