Add cauliflower and potatoes and toss around in onion mixture until coated (flavours have mixed together).
Add chicken stock so that it almost covers the cauliflower and potato. Don't add too much, it is better for it to come out thick and then add more stock at the end instead of having a watery soup.
Cover the pot with a lid and cook for approx 20 minutes until all vegetables are soft.
Puree and check consistency of soup. Add more stock if soup is too thick.