One of the trickiest parts of pulling off Thanksgiving dinner is ensuring that each of the (many, many) components of the meal are ready to eat — and are warm — at the same time. For many, deciding when and how to delegate the precious oven and stove spaces becomes a puzzle as they make mental notes of how long the turkey ought to rest, how quickly water can boil for the potatoes and at what temperature the rolls should bake. This year, however, with the help of Ina Garten, the ever-together hostess, you can tackle one key element of the feast ahead of time: mashed potatoes.