Louis Eustache Ude - The French Cook (1813)
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How's this for an opener - "Today you do and don't see cookbooks like this". You're not at all intrigued, right? Well, the point is that as a cookbook this is basically the same as ones two centuries later. Clear and detailed instructions on how to make specific dishes, organized by main ingredient. What isn't seen as often today is the sense that there's an actual person behind it. Most cookbooks today are marketed on their author whether that's a celebrity chef, some well-known food writer or just the "person who wrote that chili book". But The French Cook is, if not literature exactly, then at least aimed roughly in that direction. Ude was the son of a chef who himself worked for Napoleon's mother before heading to England where he worked for the Duke of York then at a ritz private club. The French Cook went through at least 14 editions.
As you'd expect there are things that seem odd now. Mock Turtle Soup, for instance, starts with a calf's head (in warm but not hot water) then bacon, suet, onion, eggs, lemons - the whole thing sounds like a mess. And to not waste all of the head there's a page of ways to prepare calf's brains. The ears and feet are next. Even some dishes that don't sound odd at first turn out to be not quite what you might expect. "Peas, French fashion" (p325) places an enormous emphasis on their freshness (as in picked just that morning) but then sticks them in butter, flour, onions and sugar and a couple of turns boiling water. And though a "sandwich of salad" may seem like a lost idea it's really not that different from tossing vegetables into a pita.
In short you could actually prepare food from The French Cook though whether you would want to trouble with all the sauces (and liberal use of butter) is something else.