A fantastically simple soup, perfect in spring/summer when asparagus is in season.
Heat the oil in a large saucepan. Gently fry the onion on a low heat until the onion is soft. Add the potatoes and the asparagus and let them cook in the onion for about five minutes, stirring frequently.
Add the stock and bring to the boil. Reduce the heat to a simmer and cook for about 30 minutes, until the potatoes and asparagus are very soft.
Remove from the heat and season with salt and freshly ground black pepper. Add the vegetarian Parmesan and the milk. Blend the mixture in a food processor until smooth.
Serve warm with some extra olive oil.