Have butcher cut each meat—beef, veal and pork—in a large thin slice, all the same size. Pound the meats, or have butcher do it, to make the slices thin, almost like butterfly steak. Salt and pepper the meats.
Place the pork slice and the veal slice on the beef. Roll up the meat tightly and tie with string.
Cook the onion in the lard for a few minutes. Add meat roulade and brown on all sides.
Mix vinegar with 1cup water, and pour it on the meat. Add bay leaf and cayenne pepper. Cover the pot and cook till the meat is done. If necessary add more water, but always little by little.
Take roulade out of pan. Remove bay leaf. Add sour cream to juices remaining in pan.