Grate the potatoes on a fine grater, add the flour, salt and mix well. The batter should be thick as potato pancakes. Onion cut into half rings and fry until Golden brown. Sliced boiled mushrooms, add to the onions, season with salt to taste. You can take dried mushrooms (soak for 2 hours and boil in the same water) or mushrooms (chop and fry together with the onion).

Form for baking grease, put half of the potato mass, then the mushrooms and onions and close the remaining potatoes.

Put in the oven at 180 degrees for 20 minutes. When the surface of the headstock "grab", remove from oven, spread with butter, browned and bake until tender (about I hour). That the top does not burn, it is possible to cover with foil or lower the temperature by 10-15 degrees depending on your oven. And it looks like a piece of potato grandmother