The Tartine Beurre-Confiture is the canonical French breakfast tartine, and the canon is in the order of operations: butter first, jam second, both on a single slice. The name lists the ingredients in the sequence they go on, and that sequence is the whole point. This is the slice that sits next to a bowl of coffee at the start of the day across France, the petit-déjeuner tartine that everything else in the morning repertoire is a deviation from. A jam-only version exists and gets its own treatment in the Tartine Confiture; what distinguishes this one is the butter underneath, applied with intent and not as an afterthought.
The craft is the layering, and the butter's job is structural before it is anything else. Spread cold on the bread first, edge to edge, it forms a barrier the jam cannot soak through, so the slice stays a slice instead of going to a wet patch by the second bite. The jam goes on top of that barrier, where it reads as fruit against the salt of a demi-sel butter rather than disappearing into damp crumb. The bread is usually a length of baguette split lengthwise, or a cut from a round country loaf, firm enough to take the dunk that often follows: this is one of the few sandwiches in the catalog built to be dipped, the corner lowered into coffee or chocolate until it softens and is eaten before it falls. Skip the butter and the jam goes straight into the bread and the tartine collapses; that failure is exactly why the butter layer is non-negotiable here.
The variations are single-swap and they fan out across the morning and the afternoon. Drop the jam and you have the plain Tartine Beurrée, the slice this one is built on. Swap the jam for honey and it is the Tartine au Miel; reach for chocolate later in the day and it leaves the breakfast table entirely for the goûter. The fruit itself varies by what was put up: apricot, strawberry, blackcurrant, quince, fig, whatever the household preserved. The Tartine Beurre-Confiture sits in the open-face tradition the catalog groups under Tartine, and its particular contribution is the discipline of butter before jam, which is what keeps the most ordinary breakfast in France from being a soggy one.