1. Melt the butter in a large saucepan, then add all the prepared vegetables.
2. Stir to coat and season with salt and pepper.
3. Cover the pan and leave the vegetables to sweat over a low heat for 10 minutes, stirring occasionally.
4. Add the vegetable stock and the milk.
5. Bring to the boil, then turn the heat down low and simmer for 20-25 minutes, or until vegetables are cooked.
6. Check the seasoning before serving.
7. Serve with chopped herbs, grated cheese and crusty bread.