In a very hot wok, or large soup pot, add the sesame oil. When the oil shimmers, add the celery, onion, carrot, and garlic and sauté until caramelized (about 10 minutes).
Mix the granulated soup bases in 2 cups of boiling water and stir until dissolved. Once the vegetables get a deep golden-brown color, carefully add the soup base mixture. Simmer for 3 minutes.
Add an additional 6 cups of water and the peppercorns. Bring to a boil, reduce heat and simmer, covered, for 45 minutes.
Using a fine mesh sieve or Japanese skimmer, remove all the vegetables and peppercorns from the soup until the broth is clear. Discard vegetables.
Add the mushrooms and scallions and simmer an additional 3 minutes.
Serve in soup cups and top with fried onions.
