Potpies dominate the microwave meals section of the grocery store freezer, but making them at home requires just a little more effort for an infinitely greater result. Though commonly filled with leftover chicken or turkey, potpies adapt to nearly any combination of ingredients, with a few basic ground rules. You need a combination of meat and vegetables, a thick gravy, and some type of pastry at least on top. This recipe uses canned tuna but lets you choose your favorite accompanying vegetables; you can go with the classic corn, carrots, green beans, and peas, or throw in some broccoli, cauliflower, or mushrooms.