Crockpot Carmelized Onions

3 pounds of Vidalia or other sweet onions, peeled and cut into 1/8 inch to ¼ inch thick slices
8 tablespoons butter

Place the onions and butter in slow cooker, put lid on and cook on low for 8-12 hours, until the onions are deep brown and very soft. It is almost impossible to overcook these; make sure to let the onions cook until they are mahogany colored. Makes 3 ½ cups.