In a large saucepan coated with cooking spray, saute onion and garlic until tender. Add the asparagus, broth and red pepper flakes. Bring to a boil. Reduce heat; cover and simmer for 10-15 minutes or until asparagus is tender.
Place a third of the mixture in a blender; add cream cheese, sour cream and dill. Cover and process until smooth; return to pan. Cook over medium heat until heated through. Sprinkle with nutmeg.