How to Make It
Make the lamb Preheat the oven to 325°. In a large enameled cast-iron casserole, heat the oil. Season the lamb with salt and pepper. In 3 batches, brown the lamb over moderately high heat, turning once, about 10 minutes per batch. Transfer to a plate. Add the onions, carrots, celery, garlic, thyme and bay leaves and cook over moderate heat, stirring occasionally, until the vegetables are softened and golden, about 15 minutes. Add the tomato paste and cook, stirring, until it begins to darken, about 1 minute. Add the sherry vinegar and cook, scraping up any browned bits. Return the lamb to the casserole along with 6 cups of water and bring to a simmer. Cover and braise in the oven for about 2 hours, or until the meat is very tender. Uncover and let cool for 30 minutes.
Transfer the lamb to a large rimmed baking sheet. Strain the braising liquid through a sieve into a medium saucepan, pressing on the solids; discard the solids. Skim off the fat. Boil the liquid over moderately high heat until thickened and reduced to 2 cups, about 25 minutes.
Meanwhile, make the pepper paste In a medium bowl, cover the chiles with boiling water and let stand until softened, about 30 minutes. Drain, reserving 1/2 cup of the soaking liquid. In a medium skillet, toast the caraway, coriander and cumin seeds over moderately low heat until fragrant, about 2 minutes; let cool. In a spice grinder, grind the seeds to a powder. In a blender, puree the ground seeds with the chiles, garlic, oil, hot sauce, Sriracha and vinegar, adding the soaking liquid a tablespoon at a time as needed, until smooth.
Whisk 1/2 cup of the pepper paste into the reduced braising liquid. Shred the lamb necks, discarding the bones and cartilage. Add to the braising liquid; season with salt.
Assemble the roti In a medium bowl, mix the yogurt with the lemon zest and juice. Season with salt. Pile the lamb on the warm roti. Drizzle with the lemon yogurt and top with mint, dill, cucumber, onion and cracked pepper; serve.