Preheat the oven to 400F.
Trim the stem and any leaves off the base of the cauliflower and put it in a small baking dish or oven proof skillet, or on a small baking sheet. Rub it all over with oil and curry powder or paste, and sprinkle with salt. Roast for 40-60 minutes, or until deep golden and tender when poked with a knife.
Meanwhile, heat a drizzle of oil with the butter in a small skillet set over medium-high heat and sauté the onion for a few minutes, until soft and starting to turn golden. Add the garlic, ginger and cilantro and cook for another minute or two.
Stir in the curry paste and cream and bring to a simmer; cook, stirring, for a few minutes or until thickened. Spoon around the roasted cauliflower, or save it to spoon over each wedge.