Trim the roots and tops of the salsify and peel with a vegetable peeler. cut crossvise into 2 inch long pieces and keep in a bowl of water with lemon juice to prevent discoloring. Place flour in medium saucepan and whisk in cold water, lemon juice, 1 teaspoon salt and salsify. Bring to a boil, reduce the heat, cover and cook until tender about 15 minutes. Drain. Mox the butter with mustard, combine with salsify. Season with salt and pepper. Sprinkle with parsley and serve.