Thoroughly wash all vegetables to remove soil, keeping skins on for maximum nutrient density.
Place the onions, carrots, celery, garlic, ginger, turmeric, shiitake mushrooms, peppercorns, and kombu into a large 8-quart stockpot.
Add the apple cider vinegar and cover ingredients with 4 liters of filtered water.
Bring the mixture to a boil over high heat, then immediately reduce to the lowest simmer setting.
Simmer uncovered for at least 120 minutes to allow the liquid to reduce and bioactive compounds to extract.
Add the fresh parsley during the final 10 minutes of the simmering process.
Strain the broth through a fine-mesh sieve or cheesecloth into a heat-safe container, discarding the spent solids.
Allow to cool before refrigerating or serve immediately with a pinch of sea salt.