Mushrooms have to be steamed only for a few minutes not to loose nutrients!
Boil a little slightly salted water in a pan with a lid. Add the mushroom caps without the stems and stir. After three or four minutes place in a sieve to drain.
Bring 2 litres of salted water to the boil in a medium-sized pan. If the mushrooms are too large, cut into halves or quarters while raw. Put the mushrooms into the boiling water a few at a time. After three or four minutes remove with a slotted spoon and allow to drain.