Seconding Ruhlman's Twenty, it's the book that really taught me how to cook. By focusing on techniques, it allows you to understand that when a recipe says "saute onions on medium-high heat", it really means to sweat them, and what that looks like. So rather than mechanically doing what the recipe says, you understand how the ingredients respond to different treatments, and how to get the results you want based on your equipment. And when watching a cooking show, you can see what the ingredients are doing and understand why, so that you can fill in the inevitable gaps.