Preheat oven to 400° F. Filling: Cook ground beef in a large skillet until brown; add onion and vegetables. In a small bowl, whisk together beef broth, corn starch, ketchup, Worcestershire and spices. Add to beef mixture, lower heat and simmer mixture for 15 minutes, stirring occasionally. Place into 2-quart baking dish (can also use 9×13-inch baking pan). Potato Topping: Cook diced potatoes as for mashed potatoes, in water on top of stove. Boil at least 15 minutes and test for doneness. When potatoes are tender, drain and add butter and milk. You may also season with salt and pepper to taste if you like. Mash potatoes until smooth and fluffy. Spread on top of beef filling and sprinkle with grated Cheddar cheese. Bake for about 25 minutes, until top is brown.