Learned about this technique from a historian and played around with it with great results. The recipe is not my own so I will just familiarize you with the concept.
I started with several pounds of assorted fungus and salted them heavily, close to four table spoons of kosher course ground salt was mixed to each pound of mushrooms, a few bay leaves were added along with two large onions diced and 2 tablespoons raw horseradish (prepared would be fine as vinegar is used later). Clove, garlic, black pepper, cinnamon, lemon zest, paprika, and any other common spice I looked at was added 1 teaspoon each.
This was mixed well and allowed to sit in fridge overnight to allow the salt to draw out all the moisture from the onion and mushroom, if this doesn't appear to be happening more salt should be added.
After waiting 24 hours the mash was mixed with 1 cup of apple cider vinegar and heated to a simmer, this was allowed to simmer for 10–20 minutes. After heating the mixture was strained. The high salt content and vinegar should make refrigeration unnecessary.
This "mushroom ketchup" is better than any steak sauce or fish sauce or soy sauce I've ever had, super complex flavors while being ultra familiar. The material that was left over after the strain can be dried ground and used as a seasoning as well. Please play around with this technique, if I achieved such awesome results just goofing off more competent cooks could really create something special.