NYT Cooking: This casserole may upset some mashed potato purists, but take heart: one bite and they'll be won over. The genius of this recipe, besides its utter deliciousness, is that it can be made the day before, or even two. Cook the potatoes, assemble the casserole, wrap tightly and store it in the refrigerator. When dinnertime comes, dust it with the cheese, butter and bread%2...
