Heat the butter and oil in a large saucepan until foaming. Fry the asparagus tips for a few mins to soften. Remove and set aside.
Add the onion, asparagus stalks and garlic, and cook for 5-10 mins until softened but still bright. Stir through the spinach, pour over the stock, bring to the boil, then blitz with a hand blender.
Season generously and add cream. Ladle into bowls and scatter the asparagus tips over each. Drizzle with olive oil and serve.