In a large bowl mix together yogurt, besan, turmeric powder, salt, black pepper powder and four cups of water and mix well.
Heat butter in a non-stick pan. Add cumin seeds, mustard seeds, dry red chillies, hing, onion and ginger and saute till onion becomes translucent.
Add the yogurt mixture and mix well. Bring it to boil stirring continuously.Add sprouted moong and sprouted kala chana and cook for ten to fifteen minutes on low heat.
Add tomato sauce, green chillies and coriander leaves and cook for more two to three minutes. Serve hot sprinkled with chaat masala