In a bowl, combine chicken with all of the ingredients for the chicken marinade; let marinate for 2 hours (or overnight if time allows). Heat oil in a Dutch oven. When the oil is hot, add chicken pieces in batches - do not crowd the pan. Fry until browned for about 3 minutes per side. When all the chicken is charred, set aside and keep warm. The chicken will finish cooking in the sauce.

In the same Dutch oven, heat the butter on medium heat. Saute the onions until they start to soften (about 5 minutes). Be sure to scrape up the browned bits on the bottom of the pan.  Next, add the garlic and ginger and sauté for 1 minute until fragrant, followed by adding the ground coriander, cumin and garam masala. Lt cook for about 20 - 30 seconds until fragrant, while stirring occasionally. Next, add the crushed tomatoes, chili powder and salt. Let simmer for about 10-15 minutes, stirring occasionally until sauce thickens. You are looking for a deep brown red color with the sauce. Remove from heat, scoop mixture into a blender in batches and blend until smooth. You may need to add a couple tablespoons of water to help it blend. Pour the puréed sauce back into the Dutch oven. Next, stir in the cream, sugar and ground fenugreek into the sauce. Add the chicken with juices back into the pot and cook for an additional 8-10 minutes until chicken is cooked through and the sauce is thick and bubbling. Garnish with chopped cilantro and serve with over basmati rice.