Divide the cauliflower into florets and cook for about 10 minutes until al dente. Retain some cooking water when draining.
Pour cauliflower into a bowl, season thoroughly with salt, freshly ground pepper and nutmeg.
For the dressing, mix balsamic vinegar and mustard together. Add 3 tablespoons of the cooking water and 3 tablespoons of oil. Add the finely chopped onion, chives cut into rolls and the teaspoon of sugar, mix thoroughly.
Pour the sauce over the still warm cauliflower and carefully mix in with two spoons. Mix carefully as it cools down.
The cauliflower salad can be prepared the day before - it actually tastes even better!