1Combine salt, pepper and garlic and rub the mixture into the surface of the beef.
2Place the beef in a roasting pan, fat side up, and roast for 1 hour.
3Reduce the oven temperature to 400 degrees and continue roasting for about 1 1/2 hours, or until a meat thermometer inserted in the center of the meat registers 130 degrees for medium-rare or 140 degree for medium.
4About 30 minutes before the roast will be done, begin preparing the mushrooms.
5Soak the dried mushrooms in the warm water until they are completely soft and completely rehydrated, about 15 minutes.
6Squeeze out the mushrooms, rinse well, and set aside.
7Strain the soaking liquid through a coffee filter.
8Combine the strained soaking liquid and the beef broth in a saucepan, place over high heat and reduce to 1 cup; set aside.
9Saute the leeks in butter in a large deep skillet until softened.