I make this but a little different. I use bouillon powder instead of the premade broth and add cubed cheddar in the blender before I puree the whole thing. I've also made it and kept the cauliflower as the base veggie, but also added spinach, zucchini, broccoli, mushrooms...
This soup is great for after dental work or when you're sick or for those cold winter days when you want a nice bowl of hot soup. My kids LOVE this soup, too, so I make triple batches -- good way for them to get their veggies in, too
As for amounts, I use 4-5 cups of water, add 1 tbsp of chicken bouillon powder (like OXO) and 1/2 - 3/4 of a head of cauliflower. Cook until soft. In the mean time, add 1/4 cup each of heavy cream and cubed cheddar chunks (sharper the better) and some pepper to your blender. When the cauliflower is really soft, pour the whole potful (broth and all) into the blender and puree for about 30 seconds. OMG, this is soooo good! If you're adding other veggies, just throw them in with the cauliflower and increase the broth/cream/cheese as needed.
You could use a lower fat milk/soy/etc. but it will be thinner/less creamy, of course. The cauliflower is what helps make it nice and thick so it should still be great. Oh, BTW, if you're not big on cauliflower you don't taste it much. Have fun and experiment with different ingredients (including bacon bits, different broth flavours, bits of chicken or beef, all kinds of veggie combinations).