Dust fish with seasoned flour. Add some salt and pepper and the egg to the shredded potatoes and mix well. Press a 1/2-inch layer of potatoes onto the top of each fillet. Heat oil in a large non-stick skillet over medium-high heat. Carefully place the fillets, potato side down, into the hot oil. Cook for 3 to 4 minutes or until medium-brown. Carefully flip fillets over and add remaining ingredients except butter to pan. Cook for another 3 to 4 minutes or until fish is just cooked. Transfer fish to plates and increase heat in pan to high. Reduce liquid in pan to a few tablespoons, remove pan from heat and whisk in chilled butter until melted. To serve, drizzle sauce over fish.