Tear off enough foil to completely cover meat and vegetables. Place meat in center of foil on cookie sheet. Spread onion soup mix on top. Place chunks of pared carrots and potatoes on meat. Dot with butter. Seal foil around entire thing to hold in meat juices. Bake at 350 degrees for 1 to 1 1/2 hours until vegetables are soft. The meat juices may be used to make a delicious gravy. Serves 4.