2 medium clove garlic
1/2 teaspoon dried thyme
7-1/2 pounds leg of lamb (7-8 lbs.)
1 pound large shallots
Salt
Fresh ground black pepper
2 tablespoons oil
1 cup fresh lamb or beef stock
OR
1 cup canned beef broth
1/3 cup dry red wine
1 tablespoon sherry vinegar
2 tablespoons butter
Peel and thinly slice the garlic and toss it with the thyme in a small bowl. With a small, sharp knife, remove the aitch bone and truss top of the leg to restore its shape. Cut shallow, evenly spaced incisions on both sides of the leg and slip a sliver of thyme-coated garlic into each incision. Transfer leg to a shallow baking dish and set aside at room temperature for at least one hour (can cover and refrigerate overnight.)
Peel and trim the shallots and break into separate bulbs and set aside.
If refrigerated, bring lamb to room temperature. Sprinkle with salt and pepper and rub with oil. Adjust oven rack to low position and heat oven to 450:F. Sear lamb 15 minutes, then lower heat to 350:F. Scatter the shallots around the lamb in the baking dish and roast, stirring the shallots occasionally, until the internal temperature of the lamb at the thickest point reaches 130:F, about 1 hour.
Transfer the roast to a carving board or a large platter and cover with a tent of foil.
Transfer the shallots with the pan juices to a medium saucepan. Add the beef stock, red wine and vinegar, bring to a simmer and skim. Simmer over medium-high heat, mashing the shallots with a wooden spoon, until stock is reduced to 2 cups, 10-15 minutes. Force shallot mixture through the medium blade of a food mill or puree in a food processor fitted with the metal blade. Return purie to the saucepan, season with salt and pepper, and whisk in the butter over low heat. Remove from heat, cover, and keep sauce warm.
SERVING:
Carve slices from the lamb and pass the sauce at the table.