In a large skillet over medium-high heat, cook steaks in butter until meat reaches desired doneness (for medium-rare, a thermometer should read 135°; medium, 140°; medium-well, 145°). Season with salt and pepper. Remove and keep warm.
In the same skillet, cook plums and onions for 2-3 minutes or until plums are tender. Add marmalade and vinegar; cook and stir until heated through. Serve over steaks.
Nutritional Facts: 1 serving equals 325 calories, 17 g fat (8 g saturated fat), 87 mg cholesterol, 273 mg sodium, 20 g carbohydrate, 1 g fiber, 24 g protein.