The Sandwich Anchoïade is defined by a paste, not a fillet. Anchoïade is the Provençal preparation of salted anchovies pounded with garlic and olive oil into a thick, pungent spread, and the sandwich is essentially that spread given a bread to carry it. The build is a split crusted loaf, the anchoïade worked across the crumb so it sinks in slightly, and very little else. This is the opposite of a layered sandwich: there is no stack of components, just an intensely savory paste and the bread it has soaked into.
The logic is the logic of a condiment promoted to a filling. Anchoïade is salty and emphatic in a way that a few whole anchovy fillets are not, because pounding the fish with garlic and oil distributes that intensity into every bite rather than leaving it in discrete strips. That sets the constraint hard: anything loud added on top competes with the paste and muddies it, so the successful version stays close to bare. The olive oil already in the anchoïade does the work butter does elsewhere, carrying the salt into the bread and keeping the crumb from going dry. The bread needs a firm crust and an open crumb, because a soft loaf would dissolve under an oil-rich spread and a tight crumb would not absorb it. A few rounds of raw vegetable, a curl of celery or a strip of red pepper, are sometimes laid alongside as a cool, crisp contrast to the heat of the garlic and salt, and they earn their place by doing the one thing the paste cannot, which is provide texture.
Variations move within the Provençal pantry rather than out of it. A scattering of small black olives doubles down on the brine. A few rounds of hard-boiled egg soften the salt and add body, pushing the sandwich toward the pan bagnat end of the southern tradition. A handful of raw crudités turns it into a vehicle for dipping as much as for stacking, which is the form anchoïade most often takes at the table. Each keeps the paste central and adjusts only the counter-notes around it. The Sandwich Anchoïade sits with the cured- and tinned-fish builds the catalog groups under Baguette Poisson, the tradition where the sea does the seasoning. Its specific contribution is fish as a spread rather than fish as a layer.