NYT Cooking: It’s immensely satisfying when you realize that a commonly bought item is easily prepared at home. Take bagels, for instance. This guide will explain how to make them, from mixing to forming, boiling to baking. The result is a traditionally chewy, crusty bagel that’s far fresher and tastier than those puffy dough rings from your average store. This recipe yields a dozen, and you’ll want to rese...