This is an excerpt from Ouverture de Cuisine
(France, 1604 - Daniel Myers, trans.)
The original source can be found at
MedievalCookery.com
Cow's udder. For cow's udder which has been well washed and cooked, & put
on a towel so it can rest well, & put it on a spit.
For the udder's sauce , take two or three pieces of toasted white bread, which are not burned at all, & take some broth with verjuice to temper the bread, & mix with four or five egg yolks, & put therein nutmeg, cinnamon, ginger, saffron, & sugar, & let it boil well together, & put it on the roasted udder.
Other versions of this recipe:
Cow's Udders (Le Menagier de Paris)