Sauté onion in butter in a medium skillet until tender; add breadcrumbs, chopped mint, orange rind, egg, 1/2 teaspoon salt, and 1/4 teaspoon pepper, stirring well. Set aside.
Spoon breadcrumb mixture into the opening formed by boning. Fold roast over breadcrumb mixture; tie securely with string. Place roast in a roasting pan. Sprinkle roast with remaining salt and pepper. Insert meat thermometer, if desired.
Bake, uncovered, at 350° for 30 minutes. Combine wine and orange juice; pour over roast. Bake for 1 1/2 hours.
Score fat in a diamond design; coat with glaze. Bake until desired degree of doneness: 15 minutes or 140° (rare); 35 minutes or 160° (medium); 1 hour or 170° (well done).
Transfer roast to a warm serving platter; let stand 10 minutes before slicing.
Skim fat from pan drippings. Discard fat, and pour pan drippings over roast. Garnish with orange slices and mint leaves, if desired.
Oxmoor House Homestyle Recipes