If you want to make Heston Blumenthal's mushroom dust, you preheat the oven to 150 degrees C.
Heat the olive oil in a large non-stick pan and add the onions. Brown them on medium to high heat for 3 to 5 minutes. You want the edges of the onions to get brown.
Take the onions out of the pan and set them aside. Add the mushrooms to the same pan and seal them on medium to high heat for 8 minutes. They should be brown and not burnt.
Add the onions back to the pan together with the potatoes.
Pour the chicken (or veggie) stock into the pan and simmer, covered, for 15 minutes.
Roast the dried mushrooms for 5 minutes in the preheated oven. Set them aside to cool down before you blitz them in a food processor or liquidizer (if you making the mushroom dust).
Process or liquidize your soup and check the seasoning. Add salt and pepper if necessary.
Decorate the soup with the Enoki mushrooms and sprinkle some mushroom dust over if you are using them and serve immediately.
Tip: the soup has a thick consistency, you can loosen it by adding some extra water or cream, if you like. It serves 2 people as a main course or 4 people as a starter.