This is an excerpt from Le Menagier de Paris
(France, 1393 - Janet Hinson, trans.)
The original source can be found at
David Friedman's website
To Counterfeit Bear Venison from a Piece of Beef. Take flank, and let it be chopped in large chunks as for loin stew, then parboil, lard and roast: and then boil a boar's tail, and let your meat boil a little, and throw sauce and all in a dish.