Heat the olive oil in a large frying pan over a moderate heat. Add the sliced onion and fry for 2-3 minutes, until softened.
Add the curry powder, chilli flakes and cumin seeds and fry for a further minute.
Add the cauliflower florets, stir well to coat in the spices, and then add enough hot water to cover the cauliflower. Bring to the boil then lower the heat to a simmer for 8-10 minutes.
Add the par-boiled potatoes and cook for two minutes, or until the potatoes and cauliflower are completely cooked.
Add the milk, season, to taste, with salt and freshly ground black pepper and heat through for one minute.
Add the coriander and chives and stir through.
To serve, spoon the curry into four bowls.