Our pared-down version of the Uruguayan steak sandwiches known as chivitos includes a shallot-olive relish that keep the flavors vibrant and punchy. We also like to dress the sandwiches with mayonnaise, lettuce, tomato, sliced hard-cooked eggs, ham and/or fried bacon—all of which are common additions in Uruguay. We liked the buttery tenderness of beef tenderloin; pork tenderloin, a less pricey alternative, also worked well. If using pork tenderloin, trim off and discard the silver skin, cut crosswise into ½-inch-thick slices and grill for about 2 minutes per side.