Sprinkle sole fillet with lemon juice and season with salt and pepper. Line a baking dish with ham, spread on it onions cut into rings, and mushrooms cut into slices. Season with salt, pepper and nutmeg. Place the fish fillet on top and sprinkle with butter flakes. Cover the dish and cook in the oven at medium heat. After about 20 minutes, pour white wine over the top and place in the oven for another 10 minutes. Sprinkle with parsley before serving.