In a 4-qt pot over medium heat, add oil, onion and salt. Reduce to low heat and simmer until onions caramelize (15-20 minutes).
Add potato, celery, carrot and vegetable stock to the pot. Cover & simmer until potato is soft (15-20 minutes). Remove from heat.
Allow soup to cool slightly. Add cashew butter, tamari (soy sauce) and soup into a blender and puree (may need to be done in batches).
NOTE: If you have an immersion blender, you can avoid the hassle of dirty-ing the blender.
Blanche cauliflower florets by submerging into boiling water for approximately 5 minutes. In parallel, soak the dulse in cold water for approximately 5 minutes in order to re-hydrate it. Drain the florets and dulse and add them to the soup. Add salt & pepper to taste and then serve.