Preheat the oven to 200°C.
In a large bowl, mix together the sunflower oil, yoghurt and rose harissa paste until combined.
Dip the whole cauliflower into the yoghurt mix, turning to coat all surfaces, including the sides and the base.
Place the coated cauliflower in a roasting tin or ovenproof casserole dish, then spoon over any remaining yoghurt mix. Cover with a sheet of foil or a lid and bake in the oven for 45 minutes.
After 45 minutes, carefully remove the foil or lid and bake for a further 15 minutes until golden brown.
Remove from the oven and scatter over the pomegranate seeds and chopped pistachios. Season generously with sea salt and black pepper and serve hot.