Roast Beef with margarine

2 tablespoons butter or 2 tablespoons margarine 1/2 cup chopped onion 1 1/2 cups diced potatoes 3 cups cubed leftover roast beef 2 teaspoons Worcestershire[...]

3 teaspoons unsalted butter or 3 teaspoons unsalted margarine 1 large onion , finely sliced 3/4 lb button mushroom , sliced 1 garlic clove , minced 1 cup[...]