Add the broth, water, reserved mushroom soaking liquid, mirin, soy sauce, vinegar, and chile paste, and bring to a vigorous simmer over high heat. (finecooking.com)
Bring the soup up to a light simmer over high heat and whisk in the chili paste or Sriracha sauce; start with 2 tablespoons to be safe, then add more as desired, and mix well to dissolve. (epicurious.com)