Preheat the oven to 220 degrees Celsius (430 degrees Fahrenheit).Place the cauliflower in a metal pot and fill until 3/4 full with mineral water. Add about 10 grams of salt per liter of water. Cover with a lid, bring to a boil, lower to a moderate boil and cook for 10-15 minutes, depending on the size of the cauliflower.Drain.Brush the cauliflower with olive oil and sprinkle with a little salt. Place in a baking dish, place the dish in the center of the oven, and bake until the top turns golden brown (about 30 minutes).Serve to the table in the baking dish. The outside of the cauliflower should be crisp and the inside as soft as butter. Separate the florets with a spoon and serve.