Charcoal-Grilled Stuffed Flank Steak

"Stuffed steak originated with Italian-American cooking as a way transform an inexpensive steak into something more exciting and colorful. But when we tried a few of the premade stuffed “pinwheels” from our local grocery store, both the stuffing and the cheese tried to make a run for it, with the cheese oozing out all over the grill, and the stuffing—which can include prosciutto, nuts, or spinach, among other things—falling out onto the grill in big clumps. We were sure we could turn this dish into an easy dinner, with tender beef and a juicy, flavorful filling that stayed in place. Thanks to its uniform shape and good beefy taste, flank steak was clearly the best bet. To guarantee the filling stayed in place, we butterflied and pounded the steak, so we were starting with the flattest and widest surface possible. As for the filling, we eliminated bread crumbs from consideration—after grilling, they contributed a taste of burnt toast. The classic Italian-American combo of prosciutto and provolone won raves for its salty savor and the way the dry cheese melted inside the pinwheel yet turned crisp where exposed to the grill. To prevent the meat from shrinking on the grill, and squeezing the centers of the pinwheels, we rolled up our flank steak, tied it with twine, and skewered it at 1-inch intervals before slicing and grilling. The twine kept the steak from unraveling, while the skewers prevented the meat from shrinking. Finally, we had stuffing that stayed stuffed and rich, smoky beef...."