Not as detailed as we would like, but interesting indeed
1.xxviii. Iten reinuisch (lit. Rhine fish) and bolcken boiled in water together with greens (kraut dar bey) or with sauces, that is good. The same fish and all smoked or dried fish may be served in a pepper sauce or with soup and greens on all fast days.
1. xxix. Item if you would make good soup, take the broth of dried root vegetables (ruben) and clarify it by pouring it off or passing it through a cloth into a pan. Add a little honey and season it with good spices and salt. Try it well and then pour it over (the bread sops).
You may improve a pea broth with this. And with all other soups (served) over toasted bread you strew on ginger. And if you would serve such a soup to people of rank (erberen lewten), strew it with sugar and serve hot fish with it dry (i.e. without sauce).
The instructions for cooking fish are too perfunctory to be of much use, which is a relief in a way because neither reinuisch nor bolcken can be identified as a species with any certainty. However, a dish of boiled greens with a clarified vegetable broth and cooked fish served over toasted sippets makes a plausible and pleasing Lenten meal.
Kraut can be any leafy vegetable, but I would go with finer greens such as spinach, orach or chard rather than cabbage to replicate this dish. It is meant for the table of the wealthy and cabbage carried the odium of poverty.
My current project are recipes from the Nuremberg Kuchenmaistrey produced around 1490. This was the earliest printed cookbook in German (and only missed being the earliest printed cookbook in any language by a few years). The Kuchenmaistrey (mastery of the kitchen) gave rise to a vibrant culture of amended and expanded manuscript copies as well as reprints spanning almost a century. The recipes seem designed to appeal to a wealthy, literate and cosmopolitan clientele.