1Spray 4- to 5-quart slow cooker with cooking spray. In cooker, mix squash, apple, onion, cinnamon, nutmeg, salt and pepper. Pour broth over vegetable mixture.
2Cover; cook on Low heat setting 7 to 8 hours (or on High heat setting 3 hours 30 minutes to 4 hours).
3Pour about 3 cups of the soup mixture into blender. Cover; blend until smooth. Pour into 8-cup measuring cup or heat-proof pitcher. Blend remaining soup mixture in 2 more batches; pour into measuring cup. Pour pureed soup back into slow cooker. Stir in half-and-half and syrup.
4If needed, increase heat setting to High; cover and cook about 15 minutes longer or unto hot. Top each serving with yogurt; sprinkle with chives.