To some, Cheddar is synonymous with Vermont, even if it is produced in several other states, too. For most, mashed potatoes are an absolute essential for a proper Thanksgiving table. Combining them seems natural, whether customary or not. Using two-year-old aged Vermont Cheddar, which is deeply flavored but not too sharp, gives these creamy mashed potatoes a subtle Cheddar presence, neither overwhelmingly cheesy nor gooey. (For everything you need to know to make perfect potatoes, visit our…