Here the spread is not a condiment but the entire filling, assertive enough to be the whole reason the sandwich exists. Tapenade is a Provençal purée of black olives, capers, anchovy, and olive oil, pounded coarse so it stays a little chunky rather than smooth, salty and oily and faintly bitter. In the sandwich it is the binder and the flavor at once: a crusted loaf is split, the tapenade is spread thick on the cut faces, and the bread is often closed on little else, sometimes a few rounds of tomato or a leaf of lettuce, sometimes nothing.
The logic follows from how concentrated the paste is. Tapenade carries salt from the capers and anchovy, fat from the olives and oil, and a bitter olive edge, so a thin smear flavors a whole length of bread and a thick one dominates it. That sets the discipline: the paste is loud, so anything added has to be mild and there has to be enough bread to absorb it. The olive oil in the tapenade soaks into the crumb and softens the bread from the inside, which is why a real crust matters; without it the loaf turns to paste along with the filling. A slice of ripe tomato is the common counterweight, its sweetness and water cutting the salt without arguing with it. Eaten at room temperature in the hand, it is a savory, oil-slicked sandwich with a long bitter finish, closer to an apéro bite scaled up than to a lunch-counter stack.
Variations stay inside the Provençal pantry. A green-olive tapenade is milder and less bitter than the black; a version with sliced hard-boiled egg softens the salt and adds body; a layer of fresh white cheese or a few anchovy fillets pushes it toward the Niçois end of the shelf. Each holds the olive paste constant and adjusts what little sits beside it. The Sandwich à la Tapenade belongs with the fish-and-brine sandwiches the catalog groups under Baguette Poisson, the tradition where anchovy and cured sea flavors carry the bread. Its specific contribution is a sandwich where the spread is not a condiment but the entire filling, and restraint around it is the only technique that matters.