01 -
Preheat the oven to 350°F (180°C, gas mark 4).
02 -
Heat 1/4 cup vegetable oil in a heavy-bottomed, ovenproof pan over medium heat. Brown the lamb shanks on all sides until deeply golden, ensuring even searing.
03 -
Add onion and garlic to the pan and cook for several minutes until fragrant and softened.
04 -
Pour in red wine, lamb or beef stock, tomato purée, and brown sugar if using. Add bay leaves and thyme sprigs. Increase heat until the mixture begins to simmer.
05 -
Cover the pan with a lid and transfer to the preheated oven. Cook for 1 hour at 350°F (180°C).
06 -
Reduce oven temperature to 300°F (150°C, gas mark 2) and braise uncovered for an additional 2 to 3 hours until the meat is tender and falls off the bone.
07 -
Carefully remove the lamb shanks from the pan and keep warm. Discard bay leaves and thyme sprigs.
08 -
Transfer the cooking liquid to a blender or food processor and puree until mostly smooth.
09 -
Return the puréed sauce to the pan, season with salt and pepper to taste, and gently warm over low heat.
10 -
Mix cornstarch with a small amount of cold water to create a slurry. Gradually whisk the slurry into the sauce, stirring continuously until the sauce thickens to the desired consistency.
11 -
Serve the lamb shanks hot, accompanied by the thickened red wine sauce prepared in a gravy boat.