Steam the cauliflower florets until tender.
Heat the olive oil in a soup pot over medium-high heat.
Add the onion and sauté, stirring frequently, until the onion is soft and translucent—about 5 minutes.
Add the garlic and cook—stirring—for another minute. Add the potatoes, carrots and vegetable stock.
Bring to a boil and lower the heat. Simmer, covered, until the potatoes and carrots are completely tender and the potatoes are falling apart.
Add the steamed cauliflower to the potato mixture.
Turn off the heat and puree with an immersion blender (or in a standard blender) until smooth.
Add the salt, Sriracha and nutritional yeast.
Cook, stirring, until warmed through. Taste for salt and add tamari as needed.