Thoroughly rinse the leg of lamb under the cold tap and dry it with paper towels. Lay the lamb in a roasting pan. Make 3 to 4 deep cuts in each side of the lamb.
In a small bowl add olive oil, ground cumin and garlic salt; mix well. Insert into the cuts and spoon the rest all over the leg of lamb. Cover with aluminum foil and stand for at least 2 hours. The longer the meat stands, the stronger the flavor will be.
Preheat oven to 425° F.
Bake for 30 minutes, then lower heat temperature to 350° F for another hour (add potatoes at this point) or until the meat is tender and cooked.
Sprinkle potatoes and sweet potatoes with salt to brown easier. Arrange all potatoes beside the meat in the last hour of cooking. When the meat is cooked, slice meat and serve with potatoes.
Make a gravy with the juices left on the roasting pan by adding the mixture of cornstarch and cold water plus some boiling water until a thick consistency is reached.
Servings: 6