Cover the washed and chopped vegetables in a saucepan with salted water and cook until they are firm to the bite. Make a sweat from the margarine and flour, fill up with the vegetable water and let it boil through. Whisk the egg with the milk and add drop by drop to the sauce. Season with lemon juice (vinegar) and finally add the vegetables.
I prepare the fricassee sometimes thicker and sometimes thinner. With the thick version I only serve bread or it is just enjoyed and with the thin version it is served with rice.