Place onion, garlic ,raisins cumin, turmeric, pepper, cardamom, cinnamon ,nutmeg and ginger in a food processor and process into a paste.
Heat oil in a large skillet over medium heat, add onion paste and sauté, stirring continuously, for about 10 minutes.
Stir masala Saute, stirring, for 1 to 2 minutes. Place chicken pieces in skillet and stir them around with the spice mixture until they are well coated.
Sauté for another 4 minutes, then pour in the tomatoes with liquid and stir. Reduce heat to low and simmer for 40 minute , or until the oil has separated from the liquid. Stir occasionally. (Note: If you simmer uncovered, the sauce will thicken; add hot water, or keep covered while simmering.)