This is a very popular dish in Portugal and the Azores (an island group off the coast of Portugal). It's not very salty, instead it's a really delicious dish with a fantastic combination of potatoes, cheese, cod and a delectable cream sauce. You'll want to plan ahead though, because the salted cod needs to soak in water for about 24 hours, to remove the salt.
Soak the dried salted cod in cold water with the skin side up for 24 hours, changing the water about 4 times. Drain and discard the water.
Preheat an oven to 350°F (175°C).
Place the cod in a pan with enough water to cover; bring to a boil and cook for 10 minutes. Remove the cod from the pan; remove and discard the skin and bones. Cut the cod into chunks and set aside.
Heat 1/2 inch vegetable oil in large skillet over medium-high heat. Working in batches if necessary, fry the potatoes in the hot oil until just cooked, about 5 minutes. Transfer to a plate lined with paper towels to drain.
Heat olive oil in a large pan over medium heat. Add onion and garlic, and cook until the onion is translucent, about 5 minutes. Add the cod and cook another 3 minutes; stir in the potatoes and cook another 1 to 2 minutes. Reduce heat to low.
Melt the butter in a large pan or over medium-low heat; vigorously stir the flour into the melted butter. Slowly stream the hot milk into the mixture while stirring; cook and stir until thick. Season with the nutmeg.
Pour the hot milk mixture into the cod/potato mixture. Add 1 1/3 cups cream; stir to coat. Allow the mixture to simmer together for about 2 minutes. Season with salt and pepper. Drizzle remaining 2/3 cup cream over the mixture; sprinkle with the Parmesan cheese.
Transfer mixture to an oven-proof casserole dish, and bake in preheated oven until the top is browned, about 30 to 40 minutes. Serve hot.