Clean the cauliflower, cut into florets and cook in plenty of salted water until firm to the bite. Drain and collect a small cup of liquid and allow to cool.
Finely dice the onion. Mix with mayonnaise, vinegar, salt, pepper, Maggi and some stock until smooth. Finely chop the parsley and add to the sauce.
Add the cauliflower to the sauce and mix. If necessary, season to taste, chill and let steep for 2 - 3 hours.