In a mixing bowl, combine the cream of mushroom soup and milk. Stir until well blended.
In a baking dish, layer the potatoes, onions, and ring bologna. Pour the soup mixture over the top.
Cover with foil and bake for 45 minutes, or until the potatoes are tender.
Remove the foil, sprinkle the shredded cheddar cheese on top, and bake for an additional 10 minutes, or until the cheese is melted and bubbly.
Season with salt and pepper to taste. Serve hot.
Notes:
This casserole is great for using up leftover ring bologna. Feel free to add other vegetables like bell peppers or peas for extra flavor and nutrition.