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 degrees 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 degrees F. or desired temperature (see below); basting with marinade very 15 minutes.
Rare - 120 degrees F.
Medium Rare - 125 degrees F.
Medium - 130 degrees F.
Remove lamb 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.
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.
* I have substituted pinot noir wine with excellent results!
Lamb Roast with Port Wine Sauce Recipe: https://whatscookingamerica.net/lambport.htm