The Mondseer Kochbuch has a section around the middle where a number of very similar recipes are grouped together. It looks as though someone drew on several related sources. These are all about fish with almond milk:
49 How to prepare a spoon dish (muos) of roast fish
You shall take a roast fish that is softened in vinegar and remove its bones. Throw it into milk that was made from almonds and mix in a little white flour and pour in a little fat. This is good. Do not oversalt it.
50 How to make a flat cake (fladen) of fish
You shall take a burned (?geprenten) or a bass or whichever kind of fish you like and throw them in almond milk mixed with flour and a cut apple and a little fat added to it. Put a little spice on a sheet of dough. Slide it in the oven and let it bake.
51 A flat cake (fladen) of fried fish (vischen gepachen)
Take fish and fry them in fat, and pour good almond milk over them that is thick. Mix it with rice flour and add a little fat, and mix it well with spices. Lay a sheet of dough on it (lay it on a sheet of dough?) and let it bake and do not oversalt it.
52 A good flat cake (fladen) or fritter (krapfen) of fish with almond milk
Take good almond milk and when the fish is boiled … and cut them into it and mix it with a little rice flour. This is good for filled fritters (gefulten krapfen).
Again, we have a rough parallel with the Buoch von guoter Spise (#56-58), but here, the differences are clearer:
55 If you wish to prepare a good spoon dish
A fried (gebacken) spoon dish of fish, for this you shall take a bass soaked (gebeizt) in vinegar and throw it in milk that is made from almonds, well mixed with rice flour, and with a little fat added and boiled up with it. This is very good. Do not oversalt it.
56 A flat cake (fladen)
A flat cake made from fish. Know which kind they are. Pike or basses thrown into thick almond milk well mixed with rice flour, and an apple cut into cubes, and a little fat added to it. Spread a little spices on a sheet of dough, slide it into the oven, and let it bake.
57 A flat cake (fladen)
If you wish to prepare a flat cake of fish suitable for fasting, take fish and fry them in fat. Pour thick almond milk over them well mixed with rice flour and add a little fat. Mix it well with spices, lay it on a sheet of dough and let it bake. Do not oversalt it.
This is obviously not quite the same thing. All the recipes are very similar, though, combining fish and almond milk with a binder (rice flour in the Buoch von guoter Spise, white flour or rice flour in the Mondseer Kochbuch) and a small quantitiy of fat. It is, of course, all quite luxurious, with high-end ingredients combined to produce a Lenten treat, but I suspect it would all be rather bland.
The Mondseer Kochbuch is a recipe collection bound with a set of manuscript texts on grammar, dietetics, wine, and theology. There is a note inside that part of the book was completed in 1439 and, in a different place, that it was gifted to the abbot of the monastery at Mondsee (Austria). It is not certain whether the manuscript already included the recipes at that point, but it is likely. The entire codex was bound in leather in the second half of the fifteenth century, so at this point the recipe collection must have been part of it. The book was held at the monastery until it passed into the Vienna court library, now the national library of Austria, where it is now Cod 4995.
The collection shows clear parallels with the Buoch von guoter Spise. Many of its recipes are complex and call for expensive ingredients, and some give unusually precise quantities and measurements. It is edited in Doris Aichholzer’s “Wildu machen ayn guet essen…” Drei mittelhochdeutsche Kochbücher: Edition, Übersetzung, Quellenkommentar, Peter Lang, Berne et al. 1999