Flat-iron steak is a broad, flat cut from the shoulder of the cow; look for a single 1½-pound piece. Blade steaks, also known as top blade, are a similar cut and are sometimes labeled flat-iron; they are sold in smaller portions and a line of gristle runs down the center of each piece. Either cut worked, but if you opt for blade, choose the thickest you can find and remove the gristle (which means cutting each steak into two pieces) before slicing the meat into strips. Salting the beef and letting it sit before applying the spice paste allows the seasoning to better penetrate the meat. The best way to check the meat for doneness is to cut into a piece at the center of a skewer; it should be medium-rare. We liked serving the suya with cucumber, tomato, cabbage and onion—cooling counterparts to the salty, piquant beef. If you prefer to make this indoors, place the skewers on a wire rack set in a foil-lined rimmed baking sheet. Broil on the uppermost rack until well-browned, about 5 minutes, flipping halfway through.