When is a duck not a duck? In Lyon

avirosemail, could it have been a duck terrine? Like a mousse, perhaps?

Could it have been a play on the word "Cannelé," the Bordeaux confection?

I once made a time-consuming recipe for "pain de poisson", in which the fish was finely grated through a mesh-wire sieve so that only the flavor was discernable after it was mixed with bakery-made white bread that I also sieved, cream, etc. This was then baked in a bread loaf and served as a main course. This was almost 40 years ago, living in France. It sounds similar.

I’m guessing (only) that the name was more about the shape - either that it reminded one of a small duck or that that style of casserole dish was locally called a canette. For instance, see this books.google link for other uses of the word, as a spool (in the local silk industry) and I also find it as a small bottle or can (of beer, for instance).

@Jane — I’m a fan of patés and creative uses of meats so I’m sure this wasn’t a terrine; it had a texture closer to pastry than to charcuterie.
@Robert - it’s curious that my recollection was of two ’n’s rather than one, and the texture of the item was certainly closer to that shown in photos of the Cannele that I see online, but this was a savory, not a sweet.
@Bets - you are probably on the right track: another way I think of describing the dish besides as a savory poundcake would be to think of the dumplings that are in chicken’n’dumplings (or even matzo ball soup) and then imagine the dumpling to be the size of a loaf of banana bread and soaked with a cream sauce instead of with chicken broth. And yellower - closer to poundcake colored.
@Laura - I think that’s a sensible guess, and I had spotted similar uses of ‘canette’ in web searches. No more or less potentially confusing than names like ‘grape tomatoes’ here in CA (what was wrong with calling them cherry tomatoes?) or the way they call wine pitchers Penguins in Buenos Aires.

But all this speculation might be tied together if - I don't know if it's culinarily possible -- you could take a batch of dough intended for the justifiably popular tapas dish croquetas de jamon and instead of making breaded croquettes out of it and frying the small pieces, you instead baked the dough in one sizable loaf pan. I'm imagining that the results might be similar to what I had in that bouchon.

At that same meal I recall that the foie gras was very high quality and served simply so that it could shine on its own, and the wine was from there in the Rhone valley but might not have been an actual Cotes-du-Rhone. I can't remember the dessert course but I'm thinking that overall this was not just a comfort-food dinner but getting close to mushy across the board :-)

Look at the recipe for quenelles. These are akin to light, airy matzo balls but they have fish or shrimp in them. You can’t see the “protein” at all. https://en.wikipedia.org/wiki/Quenelle

In your case, it was a quenelle preparation with a bit of young duck, put in a loafpan and baked—I speculate. The dough and overall preparation is finer, lighter than croquettes. Beaten egg white is involved. I once had a quenelle cooking class in Paris; mine were inedible.

BTW, if you find house-made quenelles on a menu, do try them. They are difficult to make correctly and ones from supermarkets are disastrous, so if a well-trained chef offers them, you’ll appreciate them.

Bets, I think you've come closest to solving this -- I've always thought of 'quenelles' in terms of the football shape, and enjoy how everything from sherbet as part of a dessert to baby carrots garnishing a main dish can be shaped this way - I've seen it done with two spoons for soft items and a paring knife for hard items, but if I think instead of quenelles de brochet, which I've had a few times but don't keep front of mind because I'm not a fan of anything anywhere near resembling gefilte fish, and just size it up and as the wikipedia article mentions think of a panade and then a sauce mousseline, then I think we're most of the way towards what I was eating. Yay.
It does tie into croquetas - there is a video recipe on the web where a chef insists that her grandma's recipe is the best (no surprise) and that she thinks of the basic croqueta de jamon as a thick bechamel made savory with minced onions, garlic, and jamon serrano.
That video recalled for me another delicious memory -- of a singles bar in Malaga where the croquetas were exceptionally good - I practiced my comparatives and superlatives in telling the server so, and they replied that it's because they used the end pieces from the jamon iberico and not the serrano.
Back to this canette conundrum, though: I have noticed that real made-in-house duck and goose foie gras tends to have an even fattier rim that is quite yellow. Perhaps the haute-yer restaurants are used to trimming it, but I can imagine that this canette dish's color was a reflection of the fat/richness involved, and the mousseline cream sauce I think is a match -- now I need to check if there's a version that has fresh rosemary. Rosemary goes great on steaks and lamb chops, and turns out to be great in cream sauces, too.
[stomach growls]

Interesting post! I wondered too...years ago I spent forever making Quenelles de poisson only to be roundly chastised for serving fish flavored matzoh balls. Not a big hit in our house. (My spell check changed it to “poison” and my co-diner of 25 years ago remembers that meal and doesn’t disagree).

@Laura's comment above rang a bell tonight when I was out for my evening lockdown stroll --
someone had put out some freebies and there it was:
a white ceramic oval casserole, with a lid shaped like a duck !
I did a double take -- nay, a triple take.
I checked the bottom for marks, and it says it was made here in USA CALIF,
but it still hit me like a ton of Lyonnais bricks: the dish itself is a duck.
The lid is, more accurately, like the top half of a duck, with the casserole as the body.

I hope you took this discarded canette into your home to give it the love and attention it deserves. Bon appetit.