The Sandwich Anguille Fumée is built around smoked eel, which is the rare sandwich fish that behaves more like a charcuterie than a fillet. Anguille fumée is eel hot- or cold-smoked until the flesh sets dense, rich, and dark, with an oiliness closer to smoked mackerel than to white fish and a sweetness underneath the smoke that few other fish carry. The build is restrained by necessity: a firm bread, butter, a layer of the smoked eel, and a sharp acid to cut it. The eel is treated as a delicacy here, which means the sandwich's job is to present it cleanly rather than build around it.
The structure follows from how rich the fish is. Smoked eel is fatty and intensely flavored, so a little goes a long way, and it needs an acid to stay balanced the way a fatty cured meat does. A squeeze of lemon or a few capers is the load-bearing counter: without it the oil coats the palate and the smoke turns heavy by the third bite. Butter is the right fat carrier rather than mayonnaise, because the eel already brings plenty of its own richness and a creamy dressing would pile on instead of frame. The bread wants a firm crumb and a real crust, since the eel is soft and contributes no structure, just a dense, oily layer that needs something to hold it. A herb note, dill or chive, is sometimes worked into the butter to lift the smoke. Eaten cool, in a few bites, it is a sandwich that asks the eater to treat a strong, fatty fish as the point rather than a problem.
Variations stay within the smoked-fish idea. A scrape of horseradish into the butter adds heat against the oil and is the most common adjustment. A layer of pickled cucumber swaps the lemon's acid for something with crunch. A thin spread of soft fresh cheese under the eel softens the smoke for those who find it too direct, at the cost of some of the fish's clarity. Each keeps the eel central and tunes one counter-note. The Sandwich Anguille Fumée belongs with the smoked- and cured-fish builds the catalog gathers under Baguette Poisson, the tradition where the smokehouse does the seasoning. Its specific contribution is an eel whose richness puts it closer to the charcuterie shelf than to the rest of the fish counter.