1. Heat the oil in a large stockpot over medium heat. Add the onion, celery, and carrots, cover, and cook until slightly softened, about 5 minutes. Uncover and add the water, garlic, parsley, bay leaf, peppercorns, tamari, and salt. Bring to a boil, then reduce the heat to medium-low and simmer, uncovered, for 1 hour to reduce the liquid and bring out the flavors of the vegetables.

2. Strain through a fine-mesh sieve into another pot, pressing the juices out of the vegetables with the back of a large spoon. Discard the vegetables. The stock is now ready to use. If a stronger stock is desired, return the stock to a boil, and reduce the volume by one quarter. If kept tightly covered in the refrigerator, the stock will keep for up to 3 days. Alternatively, you can portion and freeze it for up to 4 months.