Place 2 medium yellow onions, 3 stalks celery , and 4 large carrots (or 3-4 cups vegetable scraps) in base of inner pot, slow cooker, or large stockpot. Add in 3 cloves garlic, 2 dried bay leaves, 1 teaspoon whole peppercorns, 3 sprigs fresh thyme, ½ teaspoon kosher salt, 1 tablespoon tomato paste, and 1 tablespoon dried shiitake mushrooms. Cover with 8 cups cold water.
For Stove Top: Bring the mixture to a gentle boil over medium heat. OOnce small bubbles are forming along the sides of the pan, turn the heat to low, cover the pan, and simmer for 1 to 2 hours, adding up to 2 cups additional water if needed. For Instant Pot: Cook on high pressure for 15 minutes. Hit manual or pressure coo and use the +/- buttons to adjust the cook time to 15 minutes.For Slow Cooker: Cook on low for 8-12 hours or on high for 5-6 hours.
Strain the solids from the broth and discard the solids in the trash (not garbage disposal). Let the stock cool before storing in airtight containers. Use as desired.
Video
Notes
Use 3-4 cups vegetable scraps in place of whole onions, carrots, and celery.Note on Vegetable Scraps: Be sure to wash your vegetables/herbs well. Then store carrot peels, ends of carrots, wilted celery, ends of onions, onion peels. etc. in a freezer-safe bag, adding to it is needed. Feel free to add a variety of vegetable/herb scraps, avoiding cruciferous vegetables, flavorless vegetables, cilantro, basil, and/or rosemary.Dried Mushrooms: The dried mushrooms add an earthy flavor, but can easily be omitted. Or alternatively, you can also use ¼ cup fresh shiitake mushrooms or mushroom stems in place of dried mushrooms. Storage: Transfer the cooled vegetable broth to storage containers or clean glass jars and store in the refrigerator for up to 7 days. Alternatively, freeze the cooled broth in freezer-safe containers or souper cubes (my personal favorite), for up to 3 months in the freezer. Defrost the broth overnight in the refrigerator as needed.