Croque au Thon

Read down a French brasserie's croque column and the order is almost always the same: the croque-monsieur first, the croque-madame with its fried egg next, and then, a line or two down, the croque au thon. It is the house's standing answer to the table that wants a hot gratinéed sandwich without ham, and it earns its slot by changing one thing about the original and nothing else. The béchamel stays, the soft square loaf stays, the broiled cheese lid stays. Where a slice of poached ham would sit, a tin of drained tuna goes in instead, folded so deep into the white sauce that the cut shows one pale savoury cream rather than fish on bread.

That single swap is also the whole technical problem. Tuna packed in brine or oil arrives wet in a way the croque-monsieur's ham never does, so the tin gets drained twice, the flakes pressed against the lid until the last of the liquid runs off, before they are forked into a béchamel stiff enough to bind them into a paste that keeps its shape.

Spread that onto the pain de mie, scatter grated emmental over it, cap it, blanket the top with more cheese, and send the closed square under the broiler until the lid browns and the inside goes molten. Get the drain and the sauce right and it holds; skip either and the loaf sogs to a grey pad before the cheese has colour.

It is a domestic, unceremonious thing, which is most of its charm. This is the croque a home cook builds from a cupboard tin and a heel of bread on a Wednesday when there is no ham in the fridge, and the one a school canteen runs out by the tray because it costs almost nothing and lands a hot plate in front of a child. Some cooks skip the cooked sauce entirely and bind the tuna with mayonnaise and a little mustard, a faster route that trades the béchamel's smoothness for a tangier, looser filling. Either way it eats best straight off the heat, while the top still crackles, because a croque this wet slumps as it cools.

Its relatives are the rest of the named croque family, and the line between them runs through what the sauce carries. The croque-monsieur is the poached-ham original it descends from directly. The croque-norvégien swaps in smoked salmon for a colder, silkier seafood note, and the croque-hawaïen tucks a ring of pineapple under the cheese. The croque au thon is the cheapest member of that set and the one most often made at home, the seafood option a cook reaches for not from the deli counter but from the back of the pantry.

The Tin on the Menu

The croque it copies has a paper trail the tuna version never gets. Larousse Gastronomique dates the first croque-monsieur to around 1910, at a Parisian café on the Boulevard des Capucines, and Marcel Proust put one in À l'ombre des jeunes filles en fleurs in 1918, the narrator's grandmother proposing a stop for croque-monsieur and a coddled egg. The croque au thon, by contrast, has no inventor and no first appearance anyone has dated, which is what you would expect of a swap a thousand kitchens made on their own the moment two cheap things sat in the same cupboard.

The cheaper of those two things came up a separate and older track. Albacore canning began on the Île d'Yeu in 1866 and on Groix in 1873, on the same Atlantic coast where Nicolas Appert and his partner had run one of the first fish canneries at Nantes decades earlier. By the early twentieth century Groix was France's leading tuna port, more than three hundred boats working the albacore, and tinned tuna had turned from a curiosity into a shelf-stable protein in ordinary French cupboards.

That is the real condition the sandwich waited on. A grilled-and-sauced loaf could only become a tuna croque once tuna was something a cook kept on a shelf and reached for when the ham ran out, and once a brasserie could count on enough tins to print the dish as a standing line rather than a one-off. The béchamel and the broiler came from the Paris café of around 1910; the fish that made the variant possible came off boats out of Groix and the Île d'Yeu, where the canning that put tuna in every French cupboard began in 1866.