On Tuesdays the sandwich is leg of lamb, Wednesdays it's brisket with salsa verde, Saturdays it's fennel-rubbed turkey breast, and on Thursdays they offer porchetta. Porchetta is the classic Roman pork roast that can take on different forms but usually includes skin-on belly wrapped around pork loin or other pig parts (or, if you're serious, a whole boneless pig).
Eataly's porchetta is a low-fat version. The only evidence I saw of any belly was the occasional scrap of crispy, lacquered skin mixed in among the slices of pork loin. For each order the sandwich man sprinkles it with sea salt, then gives it a few grinds of black pepper and a few squirts of olive oil before wrapping it in butcher paper. It's simplicity itself—despite the lack of belly, this is a juicy sandwich that'll stain the paper before you get a few steps away. My real complaint is with the thick, crusty bread that occasionally overwhelms the otherwise ample filling. A more-than-hefty regular size goes for $11.80, while the large edition sells for two bucks more.
Eataly, 43 E. Ohio, 312-521-8700, eataly.com