Peel the mushrooms, remove the legs.
Cut the onion and legs into small cubes and fry in butter. Cool down.
Hard-boiled eggs, peel and cut into cubes.
Add the fried onion and mushrooms, grated cheese (leave a little for sprinkling), mustard and spices. Mix thoroughly.
Lower the mushroom caps into the milk (only the outer part).
Roll in breadcrumbs and place in a greased baking dish.
Fill the mushroom caps with egg mass, sprinkle with cheese.
Place in a preheated 180*C oven for 20-25 minutes.