Melt butter in a deep skillet over medium heat. Add onions and garlic. Cook slowly, stirring often, until onions are tender, about 5 minutes. Add gingerroot, chili powder, turmeric and cinnamon. Cook 1 moreminute. Add undrained tomatoes, tomato paste, brown sugar, salt and pepper. Reduce heat to low. Cover and simmer for 10 minutes, stirring occasionally.

Add cut-up chicken, cream and sour cream. Simmer uncovered for 5 more minutes. Remove from heat and stir in cilantro. Serve over hotbasmati rice if desired.