Preheat oven to 350. Spread raw cashews on baking sheet or pan. Allow to cook for 5 to 10 minutes. Check frequently and shake them a bit to stir them around a few times. Roast until toasted brown but be careful, they burn rapidly.
Heat olive oil in large stock pot and saute onions, celery and garlic for 5 minutes. Add cauliflower and salt and saute for another 5 minutes.
Add stock and enough water to cover and simmer until cauliflower is softened enough that a fork goes through easily. About 10 minutes.
Allow soup to cool and then blend the stock mix, nutritional yeast if desired, pepper flakes, and the cashews.
Return blended portions to the pot, stir together and add pepper to taste, and then cook until warm enough to serve.