The crescentina, called tigella almost everywhere outside its own kitchens, is defined by the iron it is cooked in. A small disc of leavened dough, no wider than a saucer, is set between two patterned terracotta or metal plates and pressed over heat until it sets pale and just freckled. It comes off the iron firm enough to hold its shape but soft enough to tear open along its equator, and that split is the entire sandwich logic. The crescentina is not bread you fill so much as bread you halve and clamp around something hot. In Modena, where it belongs, it arrives at the table in a stack still warm from the press, and the filling goes in at the table, by hand, one disc at a time.
The craft is in the size and the seam. The disc is kept small on purpose: a larger round would cool before it could be split and dressed, and the whole appeal is the contrast of a warm, faintly crisp shell against a cold or barely warming filling. The classic dressing is cunza, also called pesto modenese, a paste of lard, garlic, and rosemary pounded together and smeared inside while the disc still holds its heat so the fat slackens and slicks the crumb. Cured meat and a soft cheese follow, but the cunza is the move that makes a crescentina itself rather than a generic split roll. The dough is deliberately plain because the lard paste and the salume are the point, and an assertive bread would only argue with them.
The variations stay within the Modenese and wider Emilian repertoire: the disc split around prosciutto crudo and squacquerone, around salumi misti, around a wedge of soft stracchino, or dressed only with cunza and a little Parmigiano for the plainest version. There is a sweet end-of-meal habit of filling a warm one with Nutella or jam for children. Each of these is the same pressed disc met by a different filling rather than a different bread, and each deserves its own article rather than being crowded in here.