The schiacciata all'uva carried into a sandwich register is a sweet build, and that is the first thing to understand about it: it does not belong with the salumi schiacciate even though it shares their name and their flat, oil-touched dough. The base is the Tuscan harvest flatbread, a thin leavened sheet pressed out and studded through and over with small dark wine grapes, often uva fragola, their skins splitting in the oven and bleeding a winey, faintly tannic syrup into the crumb, the whole thing scattered with sugar and sometimes a little oil so it sits between bread and cake. As a sandwich it is split or folded around its own sweetness, and the defining fact is the partnership between the grape's musky, slightly resinous juice and the bread's faint salt and oil, which keep the sugar from going flat. Without the grapes it is a plain sweet flat; without the savoury, oiled dough beneath them the grapes have nothing to brace against and read as jam. The two are matched so a fruit bread eats like a contained dessert in the hand.
Making it well is about the grapes, the bake, and the restraint of the sugar. The grapes are small, ripe, and seeded, used whole and pressed into the dough so they roast and burst rather than sitting raw on top, releasing their colour and their winey juice into the crumb instead of weeping out the side. The dough is rolled thin and given just enough oil and salt to stay savoury underneath the fruit, because a schiacciata all'uva that is only sweet loses the tension that makes it interesting. The sugar is scattered with a light hand, enough to caramelise at the edges and crackle, never so much that it buries the grape's slight bitterness. Split warm and eaten soon, the crumb still holds the syrup; left to sit, it goes damp and the contrast dulls. A sloppy version uses watery table grapes and a thick sugared dough that tastes of nothing but sweet; a good one is winey, lightly sweet, and savoury at the base in balance.
The close cousins stay in the sweet Tuscan and broader Italian harvest register, each its own subject rather than a footnote here. There is the version enriched with a few walnuts or a brush of rosemary against the grapes, the autumn relative on a split pizza bianca with grapes in place of figs, and the plainer sweet flatbread used with fresh ricotta rather than baked fruit. Each is the same sweet-flat idea with one element changed, and each deserves its own article rather than being crowded in here.