Cauliflower gratin with caramelized onions in a creamy gruyere cheese sauce, cauliflower

Cauliflower, water, whole milk, caramelized onion, romano cheese (pasteurized part-skim milk, cheese culture, salt, enzymes), butter (sweet cream, salt), corn starch, heavy cream (milk), gruyere cheese (pasteurized milk, cheese culture, salt, enzymes, natamycin (mold inhibitor]), vegetable base (cooked vegetables [carrot, onion, and celery], salt, sugar, corn oil, potato flour, carrot powder), salt, onion powder, granulated garlic, nisin preparation (salt, nisin (antimicrobial]), nutmeg, black pepper, dried chives.