Directions

1. Preheat oven to 350°F. Pat lamb shanks dry, and sprinkle with salt. Heat 2 tablespoons oil in a large Dutch oven over medium. Working in 2 batches, cook lamb shanks, turning occasionally, until browned all over, 6 to 8 minutes per batch. Transfer browned lamb shanks to a bowl. Do not wipe Dutch oven clean.
2. Place 1 onion half in Dutch oven. Add stock, 4 cups water, daikon, scallions, garlic, seaweed, doenjang, soy sauce, perilla seeds, ginger, fish sauce, and peppercorns to pot. Stir to combine. Return browned lamb to pot, along with any juices from bowl. Bring mixture to a boil over medium-high. Cover and transfer to preheated oven. Braise until meat is very tender and falls off the bone, about 2 hours. Let lamb cool in braising liquid to room temperature, about 2 hours.
3. Transfer cooled lamb shanks to a baking sheet or a large bowl. Discard braising liquid, or strain and reserve for another use. Cover lamb shanks, and refrigerate until cold, at least 2 hours or up to 24 hours.
4. Whisk together all ingredients in a small bowl until well combined. Cover and refrigerate until ready to serve.
5. Toss together pea tendrils, snap peas, mint, perilla (if using), and nasturtium with 1 tablespoon hot mustard sauce in a large bowl until well coated; set salad aside until ready to serve.
6. Season chilled lamb with black pepper and additional salt to taste. Heat remaining 2 tablespoons oil in a large cast-iron or heavy-bottomed skillet over medium. Working in 2 batches, cook lamb shanks in skillet, turning occasionally to brown all edges, until lightly crisped on outside edges and meat is hot in the center, 4 to 6 minutes per batch.
7. Brush crisped lamb shanks with a thin layer of hot mustard sauce. Serve shanks topped with salad and with remaining mustard sauce on the side.