Peel, cube and cook potatoes in salted water until tender. Drain and whip with a little milk and butter. Set aside. Sauté the onions in butter until they are tender. Crumble in ground meat and cook thoroughly. Add seasonings one at a time and stir after each addition. Pour in tomato paste and sauce. Add whole tomatoes that have been cut into pieces. Simmer this mixture until rawness is cooked out of tomato products. Add peas and corn. Pour mixture into greased casserole dish and top with whipped potatoes. Sprinkle top with grated cheddar cheese. Bake in moderate oven (350 degrees) for about 30 miuntes or until mixture is bubbly. Let sit for about 10 minutes before serving.