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, salt and pepper. Serve with basmati rice, if desired.