Salt and pepper cod fillets and wrap with paper towels. Refrigerate for 30 minutes to 1 hour. Meanwhile, prepare Tartar Sauce. Mix all the sauce ingredients in a bowl and refrigerate.
Coat the fish with flour, dip in beaten egg, and then coat with bread crumbs.
Heat deep-frying oil to 350 F, and deep-fry the crumb-covered fish. You can check the temperature by dropping a bread crumb in the oil. If it comes up to the surface of the oil right after it's dropped, the oil is ready. Fry until the color turns golden brown and the fish floats in the oil, about 3-4 minutes, turning once or twice.
