Thoroughly clean the mushrooms (ceps, chanterelles, brown caps, chestnuts) (preferably with a dry brush and a knife). If necessary, rinse briefly in cold water.
Meanwhile, heat the butter in a pan, then add the finely chopped onion and mushrooms. Cover and cook for a while at the beginning, so they cook through better. Then fry until the desired brownness, stirring repeatedly.
Finally, simply serve with bread and butter or with potatoes. Already makes a complete meal, of course you can still eat meat, e.g., Serve with schnitzel or steak. But that is not necessary because the meat of the forest is already very rich in protein and suitable for a vegetarian diet.