Preheat the oven to 300 degrees F (150 degrees C).
Miso Paste (3 Tbsp)
Vegetable Oil (2 Tbsp)
Water (2 Tbsp)
in a small bowl. Set aside.
Dried Shiitake Mushrooms (1 pckg)
Kombu (4 pieces)
with your hands over a rimmed baking sheet.
Celery (1 stalk)
Garlic (1 head)
Fresh Parsley (6 sprigs)
and toss to combine.
Drizzle miso mixture over vegetable mixture and toss to coat.
Bake, tossing halfway through until vegetables are slightly shriveled and the mixture is fragrant, 60–75 minutes.
Transfer vegetable mixture to a large pot. Add
Black Peppercorns (1 tsp)
Water (16 cups)
Bring to a boil, then reduce heat and simmer, uncovered and stirring occasionally, until broth is reduced by half, 60-75 minutes.
Let broth cool, then strain through a fine-mesh sieve into a large container, pressing on solids to extract as much liquid as possible; discard solids.