Lightly coat a large saucepan with cooking spray; heat saucepan over medium heat. Add onion and garlic; cook for 3 to 5 minutes or until tender, stirring frequently.
Stir in broth, cauliflower, potatoes, carrot, ginger, and garam masala. Bring to boiling; reduce heat. Simmer, covered, about 12 minutes or until vegetables are tender; cool slightly.
Transfer vegetable mixture, half at a time, to a blender or food processor. Cover and blend or process until nearly smooth. Return pureed mixture to saucepan. Stir in yogurt; heat through (do not boil).
Season to taste with salt and cayenne pepper. If desired, garnish each serving with chives.