Cut the mushrooms into large pieces.
Add the melted butter (2 tablespoons) to the pan. Fry the mushrooms until lightly browned.
Put some of the mushrooms in a bowl.
Add the chopped onion to the rest of the mushrooms. Fry the onion until lightly golden brown.
Put the onion and part of the mushrooms in a blender and punch until homogeneous.
Add flour (1 tablespoon) to the pan. Fry the flour over low heat until golden brown.
Next, add 400 ml of milk, add salt and white pepper to taste. Thicken the sauce to the desired consistency.
Next, add the pieces of fried mushrooms.
Boil the sauce again over low heat. Then remove from heat.
The sauce can be served with pasta, boiled rice, buckwheat porridge, French fries.