In saucepan combine broth, onion, broccoli, thyme, bay leaf and garlic powder. Bring to a boil. Reduce heat; cover and simmer 10 minutes or until broccoli is tender. Remove bay leaf. Place vegetable mixture in blender or food processor. Cover and blend 30 to 60 seconds or until smooth. In same saucepan melt butter. Blend in flour, salt and pepper. Add the milk at once. Cook and stir until thickened and bubbly. Stir in vegetable puree. Cook until heated through for a warm soup. Refrigerate, covered, for several hours for chilled soup.