Clean the meat, cut into slices 2 cm thick, beat off and season on both sides with salt and pepper.
Finely chop the onion, chop the bread in a blender or grate.
At the bottom of the brazier, put a little melted butter, bay leaf, sprinkle with ground pepper. Fill the broiler tightly with layers consisting of 2-3 slices of meat, onion and grated bread. Put the remaining oil on top of the last layer and pour in the kvass.
Place the broiler over high heat, bring to a boil. Close the brazier with a lid and simmer the meat over low heat until tender, at least an hour, adding kvass as needed.
Serve the meat with boiled potatoes, basting with sauce from the roaster. Serve sour cream separately.