Wash the cauliflower and cut into florets.

Peel, wash and cut the potatoes into cubes.

Heat two pots of salted water.

Once the water boils, plunge the cauliflower in the first pot and the potatoes in the second.

Cook the cauliflower for 15 minutes and the potatoes for 20 minutes.

Once cooked, drain and let cool.

Wash and chop the green onions.

In a bowl, combine mustard and vinegar, stir, then slowly add the oil, stirring vigorously with a small whisk or fork.

Add vegetables, black olives, onion, salt and pepper and mix gently.