Preheat your oven to 375°F (190°C). Cut the napa cabbage in half lengthwise and place it on a baking sheet lined with parchment paper. Drizzle vegetable oil over the cabbage and roast for about 25 minutes until golden brown.

In a large stockpot, heat 1 tablespoon of vegetable oil over medium heat. Add minced ginger and chopped garlic, sautéing for about 2 minutes until fragrant.

Add the white fermented bean curd to the pot, cooking it for one minute while stirring constantly to infuse the flavors.

Incorporate the chopped onion, carrots, scallions, daikon radish, dried kelp, and rehydrated shiitake mushrooms. Pour in 12 cups of filtered water, ensuring vegetables are submerged.

Once the napa cabbage is roasted, add it to the stockpot. Bring the mixture to a rolling boil.

Reduce the heat to low, cover, and let the stock simmer gently for about 4 hours, stirring occasionally.

After simmering, strain the stock through a fine mesh sieve into a bowl, discarding solid pieces. Return the liquid to stockpot and season with salt to taste.