Boil potatoes until tender, then drain and mash. Mix in butter, onion and half the cheese. Season with salt and pepper; set aside. Cook carrots until tender, then drain, mash and set aside. Preheat oven to 375°F. Heat oil in a large frying pan. Add onion and cook until clear. Add ground beef and cook until well browned. Pour off excess fat, then stir in flour and cook 1 min. Add ketchup and beef broth. Bring to a boil, reduce heat and simmer for 5 min. Spread ground beef in an even layer on the bottom of a 2-quart casserole dish. Next, spread on a layer of mashed carrots. Top with mashed potato mixture and sprinkle with remaining shredded cheese. Bake in preheated oven for 20 min., or until golden brown.