Rinse the mushrooms well, clean the hat and cut into medium pieces. Pour the mushrooms into boiling, salted water, cook for about 10 minutes.
Drain the mushrooms and let them drain, then fry in a small amount of oil for about 10 minutes.
Cut the onion into half rings and add to the mushrooms, salt a little and pepper to taste, fry for another 10 minutes.
Serve the mushrooms warm.