I usually use frozen cauliflower and microwave it for 8 minutes for making it into mashed cauliflower (or in this case the base for the soup)

Put the Cauliflower in a food processor and let it churn for a bit. The goal is to let it pureed into a liquid. (you probably could use a little chicken broth for this too, I didn't but probably would be a great idea)

Chop the Broccolli up into the right sized for the soup.

Put all of it in a big pan on the stove and bring it to a near boil with the onions, yeast, and some salt and pepper, and the broccolli.

You can add the cauliflower in at anytime during this process. I usually am prepping the cauliflower as the rest of it is starting to boil.

Let it boil for a bit (no dairy so no worries of scalding). Bring to a simmer. It will eventually tighten up after about 20 minutes (I didn't time it, but it's a rough guess). If you want to force it to tighten up you can add the psyllium husk (but forewarned, it will turn the soup into a literal almost 'gelatin' like state if your too heavy handed).