Ingredients
1 (4 to 5-pound) boneless leg of lamb, rolled, tied, and trimmed of excess fat
4 to 6 cloves garlic, cut in half
4 to 5 sprigs fresh rosemary
Salt to taste
1/4 teaspoon coarsely ground pepper
1 cup ruby port wine*
Port Wine Sauce (see below)
Fresh rosemary sprigs for garnish
* I have substituted pinot noir wine with excellent results!

Directions
To prepare leg of lamb, cut 1-inch slits on all sides of the lamb. Insert garlic halves into the slits and weave rosemary sprigs in the string used to tie the lamb (some butchers may use a mesh-like material). Sprinkle with salt and pepper. Place lamb into a deep baking pan; pour port wine over lamb. Cover and refrigerate at least 1 hour or overnight (best overnight).

Preheat oven to 325.F. Remove lamb from marinade and place onto a rack in a shallow baking pan; place in the lower half of the oven. Bake, uncovered, approximately 2 hours or until meat thermometer registers 120° to 130°F or desired temperature (see below); basting with marinade every 15 minutes.

Rare – 120.F
Medium Rare – 125.F
Medium – 130.F

Remove from oven and transfer onto a cutting board; let stand 15 minutes before carving. During this time the meat continues to cook (meat temperature will rise 5 to 10 degrees after it is removed from the oven). 

To serve, transfer sliced lamb onto a serving platter and drizzle Port Sauce over meat. Garnish with fresh sprigs of rosemary. Makes 8 to 10 servings. 

PORT WINE SAUCE:
1 cup ruby port wine*
1 tablespoon butter 
* I have also substituted a red wine for the port wine. It was also delicious!

Add wine to drippings in baking pan and heat over medium-high heat, scraping loose browned bits on the bottom of the baking pan. Bring to a boil, stirring frequently until sauce is reduced to the consistency of heavy cream. (If it is reduced too much, use more port wine to make sauce the desired consistency.) Remove from heat. Just before serving, whisk in butter until blended.

Source: Linda Stradley  What’s Cooking America