For the dough: mix all the ingredients, knead dough and divide it into 25 g pieces. Roll each into a 1 mm thick flat cake, 12-14 cm in diameter. Fry the cakes on both sides in a dry, overheated frying pan. Oil the cooked flat cakes, stack-up and cover with a bowl so that they remain hot. For the filling: boil the peeled potatoes, drain the water and dry potatoes in a saucepan under low heat. Add hot milk and butter, mash potatoes and salt. Cut onion into small cubes and fry in vegetable oil until brown. Mix onion with mashed potatoes. Rinse millet and boil in 1 liter of boiling salted water until half cooked. Pour in milk, add butter and sugar. Cook until done. Place the filling (mashed potatoes or porridge) on the half of each flat cake and cover with the second half. Coat with butter. Serve hot with tea.