Once hot, add oil, garlic, ginger, and onion. Sauté, stirring occasionally for 5-8 minutes or until the onion has developed a slight sear (browned edges).
Add 1 cup (240 ml // amount as original recipe is written // adjust if altering batch size) of the vegetable broth to deglaze the bottom of the pan. Use a whisk (or wooden spoon) to scrape up any bits that may have stuck to the bottom to enhance the flavour of the broth.
Add remaining 5 cups (1200 ml // amount as original recipe is written // adjust if altering batch size) vegetable broth, tamari or soy sauce, and dehydrated mushrooms - stir.
Bring to a simmer over medium heat, then reduce heat to low and cover. Simmer on low for at least 1 hour, up to 2-3, stirring occasionally. The longer it cooks, the more the flavour will deepen and develop.
Taste broth and adjust seasonings as needed, adding more soy sauce or sesame oil if desired. Add the miso paste at this time