The Tartine au Fromage is where the open-face slice turns savory and stays cold: one slice of bread, cheese laid on it, eaten as a light lunch or with a drink before dinner rather than at breakfast. The defining move is that the cheese is not melted. This is the served-as-is version, the cheese sliced or spread onto the bread and eaten at room temperature, which is the line between it and the Tartine Gratinée, where the cheese is run under heat until it blisters. The moment is the apéro hour or the middle of the day, not the morning the sweet tartines occupy, and that occasion shapes everything about how it is built. The region recorded for this slice is Paris.
The craft is matching the cheese to a single slice that has to carry it cold. A soft fresh cheese, a thick fromage frais or a young chèvre, spreads to the edges and behaves almost like the butter on a breakfast tartine, smooth and even with the bread coming through underneath. A firmer cheese, a Comté or a Cantal, is laid in slices and gives a denser, chewier bite that wants a sturdier bread under it. The bread does the structural work either way: a cut from a country round or a length of baguette, with enough crust that a dense cold cheese has something to push against instead of folding the slice. A turn of pepper or a few walnuts is as far as it usually goes, since the cheese is the whole statement and a crowded slice buries it. Cold, it holds longer than the sweet tartines do, but it is still best soon after it is built, before the bread tires under the weight.
The variations are the surrounding family, each a single change for its own moment. Run the cheese under heat until it browns and you have the Tartine Gratinée, the warm version of this slice; lay ham and butter on a baguette length instead and it is the café Tartine Parisienne. Strip the savory topping away and it is the plain Tartine Beurrée the whole family starts from. The cheese varies across France's regional shelf, fresh to aged, soft to firm. The Tartine au Fromage sits in the open-face tradition the catalog groups under Tartine, and its particular contribution is the cold savory slice that asks the cheese to stand on its own.