Pierce squash several times with the tip of a sharp knife. Microwave at HIGH 1 minute. Cut squash in half lengthwise; remove seeds and membrane with a spoon. Place butternut squash, cut sides down, and garlic cloves in a 13 x 9-inch baking dish coated with cooking spray. Pierce squash multiple times with a fork. Bake at 375° for 1 hour or until squash is very tender.
While squash bakes, place curry powder and next 3 ingredients in a small nonstick skillet over medium heat; toast 1 minute or until fragrant. Set aside.
Peel cooked squash, and place in a food processor or blender. Remove and discard skins from garlic; add garlic to food processor. Add 1 1/2 cups chicken broth, and process until smooth.
Transfer squash mixture to a large saucepan. Stir in remaining 1 cup broth, milk, salt, and toasted spices. Cook over low heat 2 minutes or until thoroughly heated, stirring frequently.
Ladle soup into bowls. Top with sour cream and, if desired, cilantro.