Dice onion and chop garlic. Melt butter in a large saucepan and sweat the onions and garlic until soft.
Dice carrots, celery and parsnips into medium chunks. Add to the saucepan and toss well. Add 50 ml water and leave for 10 minutes to simmer, stirring occasionally. Stir in coriander, rosemary and black pepper and cook for 2 minutes.
Keeping heat low, add 1 litre water, chestnut purée and vegetable stock cubes. Stir well and simmer over a low heat for 15 minutes until all the vegetables feel tender.
Remove from heat and blend the mixture to a smooth soup.
Season to taste and thin if required with milk or water.
To serve, drizzle with a swirl of cream and sprinkle with chopped parsley and crispy bacon if liked.