Place the cauliflower, broth, chicken and diced onion into a large crockpot.
Cook on low for 5-6 hours, or until the cauliflower is soft and cooked through.
Using an immersion blender - or removing the soup and pureeing in a blender- puree the soup until it's quite smooth. (or conversely, my daughter liked it "chunky", so I took her bowl out before this step, you can leave it as is if wanted.)
Whisk in the milk, then leave to heat another 10 minutes or so.
Top with your choice of shredded cheese and parsley and enjoy!