Butter the casserole dish and salt a bit. Put potatoes in slightly boiling salted water for 10 minutes. Then dry, cool and peel. Cut into 1 cm thick circles. Layer the potatoes slightly overlapping into the prepared casserole dish. Cut meat across the fibers into 1.5 cm thick pieces. Beat the meat, salt and pepper and lay over the potatoes. Peel onion and cut into 1 cm thick half-rings. Melt 60 g butter in a large frying pan, put onion and simmer for 5-7 minutes, stirring. Then place onions together with butter over the meat. Coat heavily with mayonnaise and put in the oven preheated to 170 °C for 40 minutes. Sprinkle with grated cheese and cook again in the oven for 10 minutes until golden brown. Serve hot.