Soak the bread in the milk for 30 minutes and then squeeze out the excess milk: Mix the bread with the ground beef, finely chopped onion, egg, salt & pepper until all is well blended together. Form the mixture into small balls. Push a bit of butter into the center of each ball and press each into round, flat cakes. Roll each small cake in bread crumbs and fry in butter over low heat in a covered pan for 5 minutes on each side. When the Bitky are all fried, remove them from the pan and pour the sour cream into the pan, mixing it in well. Heat this up for 5 minutes or so, pour over the Bitky and serve.