Heat the olive oil and butter in a saucepan over a medium heat. Then add in the onion and fry for four minutes, until transparent. Take the asparagus and add it into the pan and allow to cook for a further 2-3 minutes. Add the stock, bring to the boil and then reduce to a simmer and cook for 7 minutes. Once cooked, take a hand blender and blend until smooth. Check for seasoning and add salt and pepper. As a finishing touch add a swirl of cream, or mix it through the whole soup. You can also add some croutons on top when served into a bowl, which adds a nice texture and crunch.