Cut the meat into thin even slices, sprinkle with salt and pepper, and on each slice put a layer of kascha, mixed with fried onions and seasoned with salt and pepper. Roll up the slices of beef and tie. Sprinkle with flour and brown in butter. Add enough stock to cover, and simmer very gently for 1 hour. These are served with a sauce made from the stock, thickened with a little flour, butter and sour cream.