The word pfeffer often referred to a spicy sauce, typically bound with bread, or even a dish served in such a sauce. Here are two recipes for such sauces, the second one probably taken from a different collection originally.
5 A Pepper Sauce (pfeffer)
Take a liver and roast it. Afterwards, cut off the outer part (das uss) and cut the liver into slices. And pound what has been cut off it in a mortar and add rye bread and broth and wine or vinegar. Then boil this up in a pan, that will be a pepper sauce of liver (ain leber pfeffer).
6 Black Pepper Sauce (pfeffer schwartz)
A black pepper sauce: Take toasted rye bread and pass it through with the broth and wine and vinegar so that it is (soft) enough. And spice it. And add bacon as is described before, and boil up the venison.
The first recipe is for a liver sauce that is here addressed as a pfeffer. These sauces are not unusual, and sometimes used as a preservative as well as a condiment. I suspect they have their origin in the fact that when cooking one small animal, the liver would be enough to make a sauce, but not enough for any other dish. Peopole did not buy a pound of chicken liver at the butcher then.
The second is an even more typical representative of the genre. The sauce is “black” because of the dark toasted rye bread, and it goes over boiled venison. Such sauces were typically made with the broth of the meat they accompanied, again this being sound economics. The reference to adding bacon “as is described before” (als vor ist geschriben) indicates that the recipe was copied from a different collection since no such thing is described earlier.
Bound together with medicinal, veterinary, and magical texts, the culinary recipes of Munich Cgm 384 were partly published in 1865 as “Ein alemannisches Büchlein von guter Speise“. The manuscript dates to the second half of the fifteenth century. My translation follows the edition by Trude Ehlert in Münchner Kochbuchhandschriften aus dem 15. Jahrhundert, Tupperware Deutschland, Frankfurt 1999, which includes the first section of recipes not published earlier.