Prepare a medium pot on a medium-high heat and add some oil.
Start peeling and roughly cut the onions and potato, wash and cut leek and celery, leave garlic as whole and add all to the pot; give it a stir. Leave to cook for about 3-4 minutes.
Add cold water until it covers all vegetables. Add stock cubes and bouquet garni. Turn up the heat until it starts boiling, cover the pan and leave to simmer for about 15-20 minutes.
In the meantime cut cauliflower into florets and leave on the side until vegetables in pot are softened. When ready, add cauliflower to pot, turn the heat up until it starts boiling again and then simmer another 7 minutes.