Place shiitake mushroom in a cup of hot (though not boiling) water to rehydrate.
Place cashews in a cup of hot (though not boiling) water to rehydrate.
Heat peanut oil in a large, heavy pot over medium-high heat. When oil is hot, add onion. Cook until onions are medium brown, though not burned, 3-5 minutes, stirring very occasionally.
Add garlic and ginger. Cook and stir for 2 minutes.
Add vegetable stock and kombu. When broth begins to boil, reduce to medium-low heat.
Simmer for 20 minutes.
While the broth simmers, prepare the cashew cream mixture.
Remove shiitake mushroom and cashews from the water, reserving the soaking liquid for use later.
Combine nutritional yeast, sesame oil, soy sauce, soaked and drained mushroom, soaked and drained cashews, and almond milk in a high-speed blender. Blend for 20 seconds on low. Add some of the soaking liquid from the mushroom or cashews if the consistency is too thick to blend. The mixture should be quite thick, but mostly uniform at this point.
Blend 20 seconds on medium, then 20 seconds on high.
When the broth is finished simmering, strain out the onions, garlic, ginger, and kombu.
Remove pot from heat. Stir in blended cashew cream mixture. Add water if consistency is too thick. Soup should be just thick enough to coat a spoon.
Taste some soup. Add salt as needed.