Bring a large pot of water to a boil. Add the cauliflower florets and boil for 7 to 10 minutes, or until fork-tender. Drain and set aside.
While the cauliflower boils, heat a large stockpot or dutch oven over medium-low heat. Add the celery, onion, thyme, and rosemary. Sauté for about 10 minutes, or until the vegetables just begin to soften, stirring occasionally. Add the garlic and continue to cook for about another minute or two.
Add vegan chicken-style bouillon powder and 3 cups of water, increase the heat to medium-high, and bring to a boil. Reduce the heat to low, cover, and simmer for 10 minutes.
Meanwhile, add the drained boiled cauliflower to a high-speed blender along with 1.5 cups water, cashews, nutritional yeast, lemon juice, and sea salt. Blend on high for 1-2 minutes, or until completely smooth and creamy. Don't finish salting here, wait until it's stirred into the overall soup.
Add the cauliflower mixture to the pot of soup and stir to incorporate. Reduce the heat to medium and continue to simmer for just 5 to 8 minutes, to slightly thicken and reduce. Taste and season with black pepper (20+ cranks or a couple of generous pinches) and more sea salt if desired. If you have extra lemon juice, you can also add one more splash for vibrancy.
Serve warm.