Mushroom Ketchup is a seasoning.
2 lbs edible mushrooms. Chop up. Add a 3 tbsp tablespoons of salt to the mushrooms, stir, smash, then let set 10 minutes while the mushrooms reduced. Let sit overnight covered in a non-metal container, preferably a ceramic crock. 1 Chopped onion, 2 tbsp finely ground fresh horseradish, 1 tbsp lemon zest, 1/4 tsp cloves, 1/2 tsp allspice, 1/4 cup cider vinegar, and a pinch of cayenne. Stir then simmer 15 minutes. Put clean towel in bowl, pour mixture onto cloth and into bowl, and strain all liquid out of mixture. Liquid will be the mushroom ketchup.
One may spinkle ground of leftover mushroom mixture as a spice.