Just a quick one today: Staindl uses cowberries (aka lingonberries, Vaccinium vitis-idaea) in a preserve and a sauce. This is the preserve:
To preserve cowberries (Paysselbeer, Vaccinium vitis-idaea)
ccxxvii) Break the berries off the stalks and pull off the khondel (? the remnants of the flower at the base?). Put them into a glass jar. Then take other berries and press them with a spoon so the juice comes out. Mix the same juice with clarified sugar, but see that there is more sugar (than juice). Let this boil together as long as two eggs (i.e. twice as long as to boil an egg). Cool it and pour it over the cowberries. Tie it shut and let it stand. This is very good for sick people who are very thirsty. You should give them a small amount when it is needed.
This is certainly not a standard cooking recipe: berries preserved in a sugar syrup made with their juice are a luxurious novelty. The final product is decoratively presented in a glass container, almost too much like modern jam. I doubt this actually alleviates thirst, but it is likely to taste very good indeed.
Something very like this is often served as a sauce with game today, and it is entirely possible that it was even back then. There is a specific sauce recipe in Staindl, too, and I will try to post it tomorrow.