Preheat oven to 400 degrees F. In large saute pan, over medium heat, heat oil. Add garlic and ginger and slowly cook until soft, about 3 minutes. Add chili powder, turmeric, Garam Masala and pomegranate juice. Let cool slightly. Rub chicken well with mixture and bake in a shallow baking pan for 25 minutes. Chicken will be three-quarters of the way cooked. When chicken is cool to the touch, remove bones and shred meat into 1/2-inch pieces. Set aside.
Meanwhile to make Butter Sauce: In a large skillet, heat olive oil over medium high heat. Saute onions, ginger and garlic until light brown, about 4 minutes. Add tomatoes and continue sauteing until tomatoes begin to fall apart, about 5 minutes. Add spices and continue to cook 5 minutes. Transfer to a blender and puree until smooth. Return puree back to pan and add cream and butter. Bring to a simmer and reduce for 5 minutes. Add shredded chicken and saute for 6 minutes more until chicken is cooked through. Add salt and pepper, to taste. Serve with basmati rice, if desired.
In a small saute pan, over medium-high heat, lightly toast spices beginning with cumin and coriander. Toast until fragrant, about 1 minute. Add peppercorns and cardamom and continue to toast another minute. Add cinnamon, cloves, and bay leaf and toast another minute. In a spice grinder, grind to a fine powder. Keep spice blend stored in a tightly seared container for up to 4 weeks.