Rub the saffron threads between your palms into a small bowl. Add the broth powder, onion, and raw garlic (if using).
Pour the boiling water on top and stir. Cover and let steep for 5 minutes.
In a food processor or blender, purée the saffron mixture, plum tomatoes, roasted garlic (if using), cucumber, and roasted pepper.
Transfer to a glass storage container and stir in vinegar, and salt and pepper to taste. (The gazpacho should have a slightly acidic edge.)
Cover and chill before serving. Garnish with chives.
Servings: