The panino con stracciatella is a sandwich built around the spill. Stracciatella is the inside of a burrata: shredded fresh mozzarella curd torn into ribbons and loosened with cream, the soft heart that pours out when the pouch is cut. On its own it is barely a solid, which is exactly what defines this panino. There is no slice to layer and no wedge to cut; there is a loose, milky, faintly sweet mass that floods into the bread and has to be contained rather than stacked. The whole sandwich is an exercise in holding a near-liquid cheese in place long enough to eat it.
The craft is structure against flood. The bread has to be sturdy and is usually lightly toasted or grilled, because a soft untoasted roll turns to paste the moment the cream touches it. The stracciatella is drained of its loosest liquid and spooned, not spread, so it sits as a bank rather than a puddle, and assembly happens at the last possible moment, ideally to order, since a panino made even half an hour ahead arrives soggy at the cut edge. The flavour is delicate and lactic, so it wants either nothing or a single quiet partner: a few leaves, a turn of pepper, a thread of good oil, a Puglian tomato. The temperature matters as much as anything; cold from the fridge it is mute, so it is brought up to cool room temperature where the sweetness and the cream actually read.
The named variations are mostly about what single thing is allowed to meet the cream. There is the version with a Puglian pomodoro, the one with a leaf of basil and oil that reads almost as a deconstructed caprese, and the build where salt-cured anchovy becomes the lead counter, which is a distinct enough idea, the Panino con Stracciatella e Alici, to stand on its own. Its parent cheeses, the whole burrata and the spreadable stracchino, follow their own logic and deserve their own articles rather than being crowded in here.