Peel potatoes and cut into quarters. Boil potatoes in salted water on med for 10 minutes or until tender. Drain and return to pan. Add milk and sour cream and mash potatoes to desired consistency. Set aside. Brown ground beef/turkey mixture (season to taste). Steam mixed veggies and add to beef mixture when finished. Preheat oven to 300 degrees. In a casserole dish, add beef/veggie mix as the first layer. Then add a layer of mashed potatoes, then top with a layer of mild cheddar cheese. Alternate these layers once or multiple times depending on the size of your casserole dish. Top layer should be cheese. After layering, place dish in oven for approximately 5-7 minutes or until cheese melts. Allow to cool for 5 minutes before serving.