Divide the cauliflower into florets and cook until al dente - but not too soft! Remove from the boiling water. Boil onion rings, fresh dill, mustard seeds and 1 tablespoon of salt, 1 1/2 tablespoons of sugar and vinegar per liter of water (vinegar to taste - approx. 150 ml to 1 liter). Pour over the cauliflower and chill.