With a mortar and pestle, grind together the ginger, garlic and chili powder -- this is called masala. Marinate the chicken with ground masala, garam masala, lime juice and salt and set aside for 1 hour.
In a clay pot, heat the butter, fry the sliced tomatoes for few minutes, and then add the marinated chicken and sugar. Cover and cook till tender.
Add the cream and serve hot. If you like cilantro, garnish with fresh leaves.