Clean the salsify under running water. Peel them with a peeler. Cut them into pieces and put them in water mixed with half of the vinegar.
Also clean the carrots, scrape or peel them and cut them into pieces.
Boil plenty of water with iodized salt and the remaining vinegar. Cook the carrots and salsify for about 20 minutes.
Preheat the oven to 200 °C. Mix egg, egg yolk, sour milk, clear soup and half of the cheese. Season with pepper and nutmeg (freshly grated).
Grease the gratin dish with a little butter. Pile the vegetables into it, pour the egg mixture over them and sprinkle with the remaining cheese. Bake for about half an hour until golden brown.
Info: Per unit about 243 kilocalories, 16 g egg white, 14 g fat, 12 g carbohydrates and 38 g fiber.