Step 1Heat 2 tablespoons of the olive oil in a large, deep skillet over medium-high heat. Dust the lamb shank with the flour (reserve any remaining flour) and brown on all sides, about 7 minutes. Remove the lamb from the skillet, reduce the heat to medium and add the remaining tablespoon of oil. Add the onion and cook until tender and lightly browned, about 5 minutes. Add the garlic, brown sugar, vinegar, bay leaf and thyme. Stir to dissolve the sugar. Add any remaining flour.
Step 2Gradually add the broth and beer to the mixture and bring to a boil. Scrape up any browned bits. Reduce the heat to low and return the lamb to the skillet. Cover and cook over low heat until the meat is tender, about 2 hours. Season to taste with salt and pepper. Remove the bay leaf.
Step 1Heat the olive oil in a small saucepan over medium heat. Add the garlic and cook 1 minute. Add the chicken broth and bring to a boil. Stir in the couscous and cover the pan. Turn off the heat and set the couscous aside until the broth is absorbed, about 5 minutes. Add the mint. Season to taste with the salt and white pepper. Fluff up the couscous with a fork.
Step 2Spoon the couscous into a serving dish. Top with the lamb and skillet juices. Carve the lamb at the table. Serve hot.