Place potatoes in a greased 15x10x1-in. baking pan. Drizzle with oil and sprinkle with chives and 1/4 teaspoon salt; toss to coat. Bake, uncovered, at 425° until tender, 25-30 minutes, stirring occasionally.
Meanwhile, in a large skillet, saute onions and mushrooms in butter until tender. Add the garlic, rosemary, pepper and remaining 1/2 tsp. salt; cook 1 minute longer. Stir in wine. Add beef and gravy; heat through. Serve with potatoes.