This is an excerpt from Enseignements qui enseingnent a apareillier toutes manieres de viandes
(France, ca. 1300 - D. Myers, trans.)
The original source can be found at
MedievalCookery.com
For sheep - Fresh sheep, in winter and in summer, must be cooked with sage and hyssop and parsley, and eaten with green sauce; Salted with mustard. And which when roasting the flanks, can be eaten with the aforementioned sauce.
Other versions of this recipe:
A lamb of another sort (Das Kuchbuch der Sabina Welserin)
A Dish of Auhashi of Fat Ram (An Anonymous Andalusian Cookbook)
AUXERRE MUTTON (or Supper Mutton) (Le Menagier de Paris)