Put the ginger and garlic pastes, half the white pepper, the black cumin seeds, and oil in a large shallow dish. Season with salt and mix well. Add the chicken breasts and rub evenly over to coat. Cover and allow to marinate in the refrigerator for 1 hour.
Put the yoghurt, egg white, and cream in another large shallow dish and mix together to make a smooth paste. Season with salt and add the remaining white pepper, the ground cardamom and mace, chopped chillies and coriander and mix well.
Put the chicken breasts into this second marinade and turn until they are evenly coated. Cover and allow to marinate in the refrigerator for a further 2 hours.
Prepare a tandoor or charcoal grill for moderate heat, or alternatively preheat the grill (broiler)to medium. Thread the chicken onto several metal skewers.
Roast over a charcoal grill or under the hot grill for 6-7 minutes, or until half done.
Remove the skewers from the heat and hang them up for about 2-3 minutes to allow any excess moisture to drain out completely. Put the skewers in a dish, baste with melted butter, and roast again in the tandoor, on the charcoal grill, or under the grill for a further 3-4 minutes, or until cooked.
Transfer the chicken to a plate and serve hot.