Soak cod, skin removed, in water, covered and refrigerated, for 3 days (change water twice daily). Drain, and cut into small pieces. Simmer milk, cream, garlic, and potatoes until potatoes are fork-tender, 10 to 15 minutes. Add salt cod, and simmer until tender, about 15 minutes. Reserving 1 cup liquid, transfer mixture to a large bowl. Add olive oil in a slow, steady stream, stirring until mixture is almost smooth, and adding liquid if needed. Season with salt to taste, and drizzle with oil, if desired. Serve with warm bread.