To add a festive twist to this recipe, serve the soup with sliced roasted chestnuts on top.
1. Heat the oil and butter together in a large saucepan set over a low heat. Sauté all the vegetables in the pan for 10 to 15 minutes, stirring occasionally. Add the garlic and herbs and cook for 1 minute more, then add the vegetable stock. Bring the soup to the boil, then reduce the heat and simmer for about 40 minutes, until the vegetables are completely soft. Stir in the milk, then taste it to see if the soup needs any salt or pepper. You can eat the soup as it is or you can liquidise it to make it smooth.
2. To serve, ladle the soup into bowls, garnish with some chopped fresh herbs and top with the sliced chestnuts, if using.