In a heavy-bottomed 5-quart pot over low to medium heat, saute diced bacon until crisp and golden, stirring often. Remove with slotted spoon and reserve for garnish. Reserve half of bacon fat in pot; discard the rest. Increase heat to medium, add chopped leeks to the drippings, and saute about 10 minutes, stirring often, until leeks are soft and beginning to brown. Add chicken broth, bay leaf, and potatoes. Bring to a boil, then reduce heat and simmer 10 minutes. Add corn and simmer 10 minutes longer. Using a heatproof measuring cup, scoop out 2 cups of the soup; process soup in blender until smooth. Pour puree back into pot. At this point, soup may be refrigerated for up to 24 hours.
When ready to finish, lay the fish fillets over the soup, gently push down to cover, and replace pot lid. Bring mixture back to a simmer and cook 5 minutes. Uncover, add milk, and bring to a simmer again, but do not let soup boil (milk could curdle). Add salt and pepper to taste; remove bay leaf. Stir gently, then turn off heat; leave covered another 10 minutes. At serving time, reheat gently if necessary, and flake fish with ladle. Serve in individual bowls garnished with reserved bacon bits and chopped parsley.