This recipe is from the Modern Farmer:

Ingredients

• 8 cups water
• 4 large reishi mushroom slices
• 8 to 10 shiitake mushrooms
• 1/2 cup dried chaga mushrooms
• 1 small onion, roughly chopped
• 1 cup celery with tops, roughly chopped
• 1 cup carrots, roughly chopped
• 2-inch piece fresh ginger, roughly chopped
• 1 tbsp sea salt, plus more to taste
• 2 tbsp apple cider vinegar
• 2 tbsp white or red miso paste

1. Place all of the ingredients in a slow cooker on low. Cook for 3 hours, stirring once every hour.

2. Strain contents through a sieve. Reserve broth. Discard everything except for the shiitake mushrooms, which can be saved for future dishes.