A good shepherd's pie is the definition of hearty, but it must come together in a vessel that supports its needs from start to finish. According to Danielle Turner, a highly experienced chef and cooking instructor, choosing the wrong pan is one of the most frequent mistakes everyone makes when cooking shepherd's pie. Her advice is to choose a baking dish that conducts heat evenly and gives the filling enough space to burble without erupting.
For the uninitiated, shepherd's pie is an old-school classic. It's a casserole consisting of meat and mixed veggies, topped with fluffy, mashed potatoes. According to the History Channel, shepherd's pie is a traditional Irish dish, though the British and Scottish have also made claims to it. A similar version called cottage pie, in fact, pre-dates it. The main difference between the two, as any stickler will tell you, is that shepherd's pie uses ground lamb, whereas cottage pie uses ground beef.