Ingredients

  • 2 tablespoons Dijon or coarse, sharp mustard
  • 2 tablespoons Worcestershire sauce
  • 3 tablespoons olive oil, divided
  • 4 cloves garlic, smashed but not chopped
  • 2 teaspoons reduced sodium soy sauce
  • 1 1/2 pounds flank steak
  • 1/2 cup feta, crumbled
  • 3 tablespoons plain yogurt
  • 2 sprigs dill fronds, coarsely chopped
  • 3 or 4 chives, finely chopped (optional)
  • 3 loosely-packed tablespoons coarsely chopped Italian parsley leaves
  • 1 tablespoon capers, lightly chopped, plus more to taste
  • Honey, to taste (optional)
  • Four 6- to 8-inch slices of a standard baguette or a sourdough roll, sliced lengthwise
  • Stoneground mustard, to taste
  • 1 handful lettuce leaves or arugula
  • 8 slices ripe tomato
  • Salt and freshly ground pepper, to taste

Method

  • To make a marinade for the steak, in a bowl that's just a bit larger than the steak, whisk together the Dijon mustard, Worcestershire sauce, 1 tablespoon of olive oil, garlic, and soy sauce. Using a very sharp knife, score the steak crosswise, making small slits about 1 inch apart. Place the steak in the marinade and rub it in, gently, making sure that the steak is thoroughly coated. Refrigerate for at least 2 hours, or up to overnight-the longer the better.
  • Take the steak out of the refrigerator 30 to 45 minutes before you plan to grill it. Get your grill nice and hot, at least 400° F. While it heats, make an herbed feta sauce: Mix together the feta, yogurt, herbs, capers, and remaining 2 tablespoons of olive oil. Taste for salt and add some (if any) to taste along with some freshly ground pepper. If it's a bit too sharp for your liking, stir in a touch of warmed honey and stir well.
  • When the grill is ready, put the steak on, generously sprinkle it with salt and freshly ground pepper, and let it grill, undisturbed, for 6 to 7 minutes. Flip it over, grind a bit more pepper on it, and sprinkle it with just a touch more salt. Grill without moving the steak for another 6 minutes, or until the meat reaches an internal temperature in the thickest spot of 130 to 135° F for medium-rare. Remove it from the grill, lightly tent it with aluminum foil, and let sit it for at least 10 minutes.
  • While the steak is resting, toast or grill the slices of baguette or rolls, if you like.
  • To assemble the sandwich, spread the mustard on one side of each roll. Thinly slice the steak across the grain. Layer slices onto the rolls, Drizzle directly onto the bread any juices that have collected on the plate on which the steak rested.
  • Distribute the herbed feta between the rolls. Put the lettuce or arugula on top followed by the sliced tomatoes. Put the two halves of each sandwich together.