Season the chicken breasts and coat lightly with flour. Melt 4 tbs of the butter in a large skillet. Add six breasts and cook over moderately high heat, turning once, until golden, about 4 minutes a side. Transfer to large plate and repeat with next 6 breasts.
Melt remaining 4 tbs butter in skillet. Add onions and cook over moderate heat, stirring until softened about 10 minutes. Stir in garlic and ginger and cook until slightly softened about 3 minutes. Add the ground cumin, cumin seeds, turmeric, caraway seeds and 1/4 tsp cayenne and cook for 1 minute. Stir in the crushed tomatoes and the chicken stock. Transfer to an enamaled casserole or dutch oven stew pot.
Add the chicken to the casserole and bring to a simmer over moderately low heat, simmer for 10 minutes. Stir in sourcream brown sugar, tomatoe pasted, crushed red paepper, saffron, cardamom, cloves, and nutmeg. Cover and cook over low heat 30 minutes. Uncover and cook stirring occasionally until the chicken is tender and the sauce is thickened., about 45 minutes longer. The sauce will not be completely smooth.
To FREEZE: Let cool completely, tyhen refrigerate until cold. Transfer to plastic containers covering the chicken pieces with sauce, press plastic wrap against the surface of the sauce then seal the conainers and freeze up to 1 month.
To REHEAT from FROZEN: Let thaw in the fridge for 24 hours. Remove the plastic wrap and transfer to casserole pot. Cover and rewarm over low heat stirring.