German chocolate cake is also named after somebody called German, as I understand it. But they’re all proper names, and the question in the OP is, should we capitalize proper names in food names? My answer is, why wouldn’t we? We capitalize them everywhere else.
The majority of cases where I’ve written the names of dishes were menus and recipes. I always capitalized every word of the dish, for example, French Onion Soup. But I have no idea if there is a grammatical rule. Since the name of a specific dish on a menu would seem to be a proper name, I’d assume every word was capitalized, as opposed to a generic food name, like onion soup or hamburger.
Now, see, there, I’m not even sure what the original proper noun even was. The non-proper meaning has clearly overshadowed the proper meaning. But I know that “French fried” means “fried in a manner characteristic of France”. Now, it may or may not be accurate: Maybe the folks who named French fries were confused about their actual origin. But the “French” meaning hasn’t been obscured yet.
Since most of these words are no longer associated with their original meaning, they wouldn’t be capitalized. I’m thinking that most people don’t know or care about the origins of waldorf salad. Capitalizing it would imply that it’s a salad made specifically at the Waldorf Hotel, or made by Chef Waldorf. Even if the connection were once valid, the phrase has been around long enough to exist on its own.
French fries aren’t even French; they’re Belgian. Not sure if that would affect the grammar.
If you do capitalize these things, how do you know which ones to capitalize? For example, I know Scone is a city in Scotland, and scones are Scottish, but I don’t know if the name refers to the town. I could come up several examples like that. I’m not so sure about a grammar rule that one can only correctly follow by being an expert in etymology.
What it comes down to is this - are you referring to the country or person when you name the object? When a name of an object has ceased to refer to the person or the place, then it seems to be customary to drop the capital letter.
Although a sandwich seems to have had some link to the Earl of Sandwich, we do not capitalise it.
So, french fries seems correct, as they are USAian. (In English they are called chips. What USAians call chips is called crisps in English.)
However French onion soup seems to be right, as it actually purports to be a French recipe.
Oh, for the simple days when we were all supposed to say “freedom fries” (and I assume, “freedom kissing”)! How much simpler life would be! (Really, JK. Wouldn’t want to go back to that stupidity.)
I just checked my 1989 Betty Crocker cookbook. (Also checked my 1950 BC cookbook but assumed that might be dated by now.) In the index under “Potatoes” is listed “French-fried.” There’s also a “French silk” pie. So I gather one IS supposed to capitalize the proper adjective in food names. I mean, really, if you can’t trust a cookbook from a fictional American icon, who can you trust?
In fact, there is no evidence that scones are Scottish, and the name of Scone seems to be a coincidence, not a derivation - although the good people of Scone tell a different story to gullibnle tourists. Scones are traditional food made and eaten all over the two islands of Great Britain and Ireland.
I think part of the reason they are attributed to Scotland is that where the word first makes its appearance–in 1513 in a translation of the Aeneid by Scottish poet Gavin Douglas.