Mix together mashed paneer and potatoes along with cornstarch, red chilli powder, green chilli-ginger paste, salt to taste and white pepper powder. Divide the mixture into sixteen even-sized balls. Stuff each ball with chopped cashewnuts and raisins. Heat sufficient oil in a kadai and deep fry the balls a few at a time until golden brown.
Drain onto an absorbent paper and keep aside. In the same oil, deep fry bhavnagri mirchis. Drain and remove into a bowl. Add salt to taste, lemon juice and yogurt. Mix well and leave to marinate for an hour. Grind together khus khus, remaining chopped green chillies and half of the coriander leaves. Heat two tablespoons of oil in a pan.
Add cumin seeds and add sliced onions. Sauté and add sambhar onions. Sauté for a minute. Add ginger-garlic paste, coriander powder, turmeric powder, roasted cumin powder, half of the green chillies and stir well. Sauté for two to three minutes. Add one cup of water and stir. Leave to cook on low heat for five minutes.
Add khus khus paste. Add marinated bhavnagri mirchis with marinade. Add one-fourth cup of water to the marinade bowl and add to the pan. Cook on high heat for three to four minutes. Add tomato slices and salt to taste. Add garam masala powder, sliced spring onions with greens and remaining chopped coriander leaves.
Stir well and cook on low heat for seven to eight minutes. Place paneer koftas in a deep flat dish. Pour over hot gravy and serve immediately.