There is a good reason why most Indian restaurants I’ve been to have this dish on their menus;  because it is so delicious!  It’s best to use leftover Tandoori Chicken for this, or you can whip up a new batch  to use in this recipe.  I often prepare some fresh boneless chicken, marinated in Tandoori spices and yogurt, and grill it on skewers just for this recipe if I have no leftovers on hand. After years of experimenting with many Butter Chicken recipes gathered from all over, I am most satisfied with this one.  The secret I have found is the fenugreek, for which there is no substitute.  This single spice makes the dish complete, and makes your whole house smell like an Indian restaurant. Ingredients: 10-20 pieces of Tandoori Chicken, boned and cut into bite sized pieces; or about 5 pounds of uncooked boneless chicken  (may substitute boneless Tandoori Chicken that you grill on skewers) For the sautéed base: 3 tablespoons butter 1 large yellow onion, peeled and diced For the ground spice mixture: 6 - 8 whole cardamom pods – crush the pods and remove the seeds and reserve them 2 -3 tablespoons whole fenugreek seeds  (or substitute 4-5 tablespoons dried fenugreek leaves) 6 whole cloves For the gravy: 1 can (28 oz) tomato puree 3-4 tablespoons tomato paste ½ pint (236 ml) heavy cream For last minute seasoning: ½ teaspoon ground cinnamon 2 – 3 tablespoons brown sugar 1 teaspoon salt, or to taste Optional: ¼ teaspoon red food coloring (red #4) to restore some of the the rich red tomato color that is lost after adding the heavy cream 1 tablespoon honey 2 tablespoons ginger root, peeled and chopped fine 2 –3 tablespoons ketchup.  I swear I saw this on an Indian cooking video.  I’ve tried it and am not sure about the results, so you will have to experiment ½ teaspoon ground red pepper or to taste ¼ cup crushed nuts, preferably cashews ¼ bunch cilantro leaves, for garnish Crush the cardamom seeds, the fenugreek seeds and the whole cloves into a powder using a mortar and pestle or spice grinder and set aside.  You can substitute pre-ground spices here, but....remember that the whole basis of Indian cooking is flavor from fresh spices like this.  You can substitute ground spices but grinding your own is much better for this or any other Indian recipe. If available, substitute dried fenugreek leaves for the fenugreek seeds and add them at the last moments of cooking. Melt the butter in a medium sized pot and then sauté the onion in it until the onion starts to look translucent or as soon as it begins to start browning.  Add the tomato paste and the ground spices (cardamom, fenugreek and cloves) and sauté a few moments more until the tomato paste liquefies a bit and spreads easily. Add the tomato puree, the heavy cream and any of the optional ingredients that you like except for the garnish.  Simmer for about 15-20 minutes.  Then add the last minute seasonings listed above; the cinnamon, brown sugar and salt. The gravy may have become too thick – if so you can thin it with a little water. Finally, add the chicken and continue simmering until it is warmed through then serve hot with rice and/or bread, garnished with the optional cilantro. This dish keeps well in the fridge or freezer for reheating later.  My son takes it to work often, for a flavor-filled lunch.