Heat the peanut (or neutral cooking) oil in a medium saucepan over medium heat. When hot, add the ginger and garlic. Stir until the herbs are nearly cooked through, 4-5 minutes.
Add the miso and doubanjiang. Mix it with the ginger and garlic to form an even paste. Stir until the paste is slightly browned, 3-4 minutes.
Add the cashews or cashew butter. If using cashews, stir and cook until the cashews are blended with the paste and slightly toasted, 4-5 minutes. If using cashew butter, stir until the butter is integrated with the other paste and slightly toasted, 2-3 minutes.
Pour in the sake (or water) and stir well to scrape up any bits stuck to the bottom of the saucepan.
Turn off the heat and stir in the vegetable broth.
Transfer the contents of the saucepan to a high-speed blender. Blend until the mixture is smooth and uniform, about 1 minute on high. Transfer the mixture back to the saucepan, Add the dried shiitake mushroom and kombu. Cover and heat over low heat.