Rub lamb with rosemary; salt lightly.
Pierce lamb; insert garlic in lamb.
Bake at 325 degrees for 30 minutes per pound.
Baste with orange juice occasionally.
Let pan liquid brown between bastings.
Remove lamb from oven; place on heated platter.
Remove fat from pan drippings; add salt to taste.
Blend cornstarch and 2 tablespoons water; add to pan drippings.
Cook, stirring constantly, until thickened.
Serve sauce over lamb.