lamb: trimmed of excess fat and butterflied garlic: peeled and chopped onion: peeled and thinly sliced green bell pepper: stemmed, cored, seeded, and cut into 2.5cm pieces pimientos: drained and cut into 2.5cm pieces
Preheat oven to 200°C. Season lamb with granulated garlic and salt. Transfer to a roasting pan, fat side up, and roast for 30 minutes. Decrease oven temperature to 160°C and roast for 30 minutes. Pour half the wine over the lamb and roast until internal temperature of meat registers 62°C, about 20 minutes more. Transfer lamb to a cutting board and return pan to oven to let drippings brown, 20—25 minutes. Pour off remaining fat. Add 1 1/2 cups water to pan, scraping browned bits with a wooden spoon. Bring to a simmer on topof the stove over medium heat. Combine cornstarch with 2 tbsp. water and whisk into pan. Simmer until sauce is thick, about 5 minutes, and set aside.
Saving choice cuts of lamb for another use, trim away smaller exterior pieces of meat (you should have about 907g), trim them of fat and gristle, and cut any chunks into 5cm pieces
Heat oil in a heavy medium pot over medium heat. Add garlic, onions, and bell peppers and cook for 5 minutes. Add pepper flakes and cook for 2 minutes. Add lamb pieces, remaining 1/2 cup wine, and reserved sauce, decrease heat to medium-low, and simmer stew for 45 minutes. Add pimientos, cover pot, and gently simmer stew until lamb is very tender, 2-3 hours more.