TO PREPARE THE STEAK
Hanger steak has a tough membrane running down the center. You can leave this membrane in place, trimming it away as you eat the steak, or you can remove it before grilling. The latter is my preference, as the meat is easier for guests to eat with no pesky membrane to cut around. To remove the membrane, use a boning knife or other sharp knife to slice carefully on either side of it and lift it out cleanly, with little or no meat attached. You will be left with 2 disconnected strips of hanger steak. Rearrange them side by side and tie in several places with butcher’s twine to re-create a single steak.
Combine the salt and crushed pepper. Season the meat all over with the mixture. Set a flat rack on a tray and set the meat on the rack so air circulates underneath. Refrigerate, uncovered, for at least 4 hours and up to 1 day. Remove from the refrigerator 1 hour before grilling.
Prepare a moderate charcoal fire in the center of your grill, leaving the outer rim devoid of coals so you can grill the red onions over indirect heat. Alternatively, preheat a gas grill to medium, leaving one burner unlit for indirect grilling.
Grill the hanger steak directly over the coals or gas flame, turning once, until the meat is done to your taste, about 10 minutes for rare. (Hanger steak is best if not cooked beyond medium-rare.) Let rest 5 minutes. Remove the string (if you tied the meat) and slice thinly against the grain. Serve immediately with the red onion raita.
TO PREPARE THE RAITA
Peel the onion and slice neatly into 1/2-inch-thick rounds. Carefully thread a thin bamboo skewer through each slice to hold the rings together. Brush the slices with oil on each side, and season with salt and pepper on each side. Grill over indirect heat—not directly over the coals or gas flame—turning once, until the onions are soft and slightly charred, about 25 minutes. Do not rush them or they will blacken before they are fully cooked. Transfer to a cutting board and pull out the skewers. If the outer ring of the onion slices is dry and papery, discard it. Chop the remainder of the onion coarsely.
In a bowl, whisk together the yogurt, garlic, cilantro or mint and cumin. In a small skillet or butter warmer, warm 2 teaspoons vegetable oil over medium heat. Have the skillet lid handy. When the oil is hot, add the mustard seeds. Protecting your face with the lid, cook until the mustard seeds pop and become fragrant, 1 minute or less. Pour the hot oil and mustard seeds over the yogurt and stir in. Fold in the grilled onion. Season with salt to serve.
Reprinted with permission from Yogurt, by Janet Fletcher, copyright © 2015, published by Ten Speed Press, an imprint of Penguin Random House LLC.