Wash hands with soap and water. Peel and chop the onion. Wash the potatoes well, peel, and cut into large chunks.

Bring a large pot of salted water to a boil over high heat and cook the potatoes until tender, 15-20 minutes. Drain, and mash with ¼ cup sour cream and salt and pepper.

Heat ¼ cup butter in a large oven-proof skillet over medium-high heat. Cook the onion until softened. Add the flour and season with salt and pepper. Stir until smooth, then gradually stir in 2 cups of milk, mixing until smooth. Stir in the soy sauce.

Bring the sauce to a simmer. Cut the fish into chunks and season with salt and pepper. Add the fish and the peas to the sauce, bring back to a simmer, and cook until the fish is tender, about 5 minutes.

Heat oven to broil. Remove the skillet from the heat. If your skillet is not oven-proof, transfer the contents to a greased casserole dish. Top with the mashed potatoes. Spread potatoes over the top and sprinkle with the parmesan cheese.

Broil 6-8 minutes until browned (watch closely as broilers vary). Cool for 10 minutes and serve. This recipe makes 4 servings. Refrigerate leftovers within 2 hours.