Put green onions and sliced potatoes in pot with bacon fat and cook until the green onions have softened, just a minute or two. Sprinkle flour over top and stir for another minute. Pour in milk, chicken broth, Old Bay, parsley, and cayenne pepper. Bring to a boil, stirring occasionally. Lower to a simmer and cook until potatoes have softened, about 15 minutes. Add both cans of corn and the chicken, continue cooking until everything is heated through.