Onion Purée
Cover the cipolline onions with the milk in a medium-sized saucepan and bring to the boil. Simmer for 25 minutes, stirring continuously, so the milk doesn't catch on the bottom. Once cooked, strain the onions through a sieve and then discard the milk. Purée the onions in a high-speed blender until smooth. Pour into a medium-sized plastic squeeze bottle with a fine nozzle. Keep warm ready for use.
Assembly
Reheat the cauliflower soup, then pour into a serving jug. Pour equal portions of the soup into the demitasse cups, then swirl some onion purée from the squeeze bottle over the top of each cup.