Clean the mushrooms and cut into small pieces.
Peel and finely chop the onion.
Fry mushrooms and onions, add sour cream and a little salt.
Prepare the buns: cut off the "lid" and choose the crumb.
Put the mushrooms into the cavity of the bun.
Sprinkle grated cheese on top.
Bake for 10 minutes at 180-200°C.
"Lids" must be taken out of the oven before the buns or put into the oven later, and removed along with the buns.