Simply peel the skin from the onions and cut off the roots. Use an apple corer to take out the middle of the onion. Mix the curry powder with butter and force into the middle of the onion with a spoon. Spread some butter over the outside of the onion and season with salt and pepper. Wrap in foil and place in the coals of the barbecue. Turn occasionally with long handle prongs to prevent burning and cook for around 20 – 30 minutes.