SAUCE
1 tablespoon butter
1/2 cup minced shallots (about 4 ounces)
1 cup dry red wine
3/4 cup ruby Port
1 cup canned beef broth
1 sprig fresh rosemary or 1/2 teaspoon dried
3 Tablespoons balsamic Vinegar

STEAKS
1 tablespoon olive oil
4 1-inch-thick beef tenderloin steaks (about 6 to 8 ounces each)

3 tablespoons chilled and unsalted butter
1 teaspoon chopped fresh rosemary or 1/4 teaspoon dried

FOR SAUCE: Melt butter in heavy large saucepan over medium-high heat. Add shallots and sauté until tender, about 3 minutes. Stir in wine and Port. Boil 5 minutes. Add broth, balsamic vinegar and rosemary sprig and boil until liquid is reduced to 1/3 cup, about 12-15 minutes. Strain sauce and set aside. (Can be prepared 1 day ahead. Cover and refrigerate.)

FOR STEAKS: Heat oil in heavy large skillet over medium-high heat. Season steaks with salt and pepper. Add steaks to skillet and cook to desired doneness, about 4 minutes per side for medium-rare. Transfer steaks to platter. Tent with foil to keep warm.

Add sauce to skillet and bring to boil, scraping up any browned bits. Remove from heat. Gradually add butter, whisking just until melted. Stir in chopped rosemary. Season to taste with salt and pepper.

Spoon sauce over steaks and serve