Pre-heat the oven to 450° F.
Cut the cauliflower into near bite-sized florets. Rinse them off, shake them to rid of excess water, and transfer them to your Dutch oven. Add the onion, garlic cloves, thyme, olive oil, and spices. Give everything a good stir to distribute the oil and seasonings as best as you can.
Place the Dutch oven into the oven, uncovered, for 30-40 minutes or until most of your veggies start to take on a golden color. Stir the contents of the Dutch oven every 15 minutes or so during cooking time.
When done, remove the Dutch oven and set it onto the stovetop; stir well.
Add the broth, milk, and nutritional yeast. If you have an immersion blender, use it to blend all of the contents in the Dutch oven until smooth, or until you've reached the consistency/texture you prefer. If you don't have an immersion blender or if you prefer a perfectly smooth purée, transfer the contents to a high-powered blender, like a Vitamix, and blend until smooth. Depending on the size of your blender, you may have to do this in batches.
Taste, and season with extra salt and pepper if need be, to your liking.Serve with a drizzle of pesto, walnuts, and microgreens (topping optional).