Step 1Rinse cod under cold running water to remove surface salt. Place in large non-aluminum pot, cover with water, cover and refrigerate 24 hours, changing water several times.
Step 2Pour off water, refill pot with clean water and boil cod until it flakes easily with fork, 8 to 10 minutes, depending on thickness.
Step 3Heat 3 tablespoons oil in large skillet over medium heat and saute onions until barely brown, 10 minutes. Add garlic and cook 1 minute more. Set aside.
Step 4Drain cod and let cool. Flake into large bowl and remove any bones or bits of skin. Add onion-garlic mixture, nutmeg and white pepper to taste and remaining oil. Toss lightly. Pack mixture into well-oiled 13x9-inch oven-proof casserole dish. Top with potato slices.
Step 5Lightly oil a baking sheet, place over casserole and invert. Carefully remove casserole dish to keep cod mixture intact. Cover with foil. Bake at 400 degrees 10 minutes, remove foil, then continue baking until cod is lightly toasted, about 10 more minutes.
Step 6To serve, cut a square of cod and center on each of 6 to 8 serving plates. Drizzle with additional oil to moisten. Garnish with 2 egg halves, olives and parsley.