Preheat the oven to 200C/400F/Gas 6.
Cut off the bottom 4-5 inches of the butternut squash. This will make a bowl for the soup. Remove any seeds, place on a baking tray and roast in the oven for ten minutes.
Peel and chop the remaining butternut squash. You will need 150g/5½oz.
Heat the olive oil in a saucepan and cook the garlic for one minute.
Add the chopped butternut squash and fry for two minutes.
Add the chicken stock to the pan and bring to the boil.
Simmer for 8-10 minutes, or until the butternut squash is tender.
Add the milk to the pan and season with salt and freshly ground black pepper. Allow to cool.
In a food processor, blend the butternut squash mixture until smooth and pass through a sieve into a jug. Warm through in a pan when required.
To serve, remove the butternut squash base from the oven and pour in the soup. Place on a plate, garnished with a sprig of coriander.