Poach desalted cod in milk (or water) with bay leaf and thyme 15 minutes. Drain and flake, removing all skin and bones.
Boil cauliflower until very tender. Drain and mash well.
In a food processor, blend cod, garlic, and a pinch of white pepper.
With machine running, alternate adding warm olive oil and warm cream in a thin stream, creating an emulsion.
Fold in mashed cauliflower. Adjust seasoning — remember cod is naturally salty.
Spread in a gratin dish. Drizzle with olive oil, scatter with cheese.
Broil 8–10 minutes until golden. Serve with olives, capers, and parsley.