Heat the butter and oil in a pan, fry the asparagus tips for 2mins to soften a little, then set aside. Add the onion, garlic, trimmed asparagus stalks (not tips) and chopped potato and cook for up to 10 mins to soften. Add the spinach and stock, stir, bring to the boil and whiz smooth with a stick blender. Add more water for consistency if needed. Season and serve with the asparagus tips on top, plus a dollop of Greek yoghurt if you wish.
Recipe by appetite magazine at https://www.appetitemag.co.uk/no-sin-asparagus-soup/