Combine the flour, 2 teaspoons salt, and 1 teaspoon pepper in a large shallow plate. Pat the fish fillets dry with paper towels and sprinkle one side with salt. Heat 3 tablespoons of butter in a large sauté pan (10-12 inch pan) over medium heat until butter just begins to brown. Dredge 2 fillets in the seasoned flour on both sides and place them in the hot butter. Lower the heat to medium-low and cook for 2 minutes. Turn carefully with a spatula and cook for 2 minutes on the other side. While the second side cooks, add 1/2 teaspoon of lemon zest and 3 tablespoons of lemon juice to the pan. Sprinkle with the parsley, salt, and pepper. Keep fillets warm in a 200 degree oven and make the second batch using the remainder of the sole, butter, lemon, parsley salt and pepper. When all fillets are cooked, serve immediately.