Ingredients

2 tablespoons peppercorn, medley crushed
1 teaspoon salt
3/4 teaspoon crushed dried rosemary
1 (1 1/2 lb) flank steak
2 tablespoons butter
1 onion, halved and thinly sliced (about 1 cup)
2 tablespoons balsamic vinegar
2 tablespoons whole grain mustard

Directions

Combine peppercorns, salt and rosemary.Rub both sides of steak with peppercorn mixture.In large nonstick skillet, melt 1 Tbsp butter over medium heat. Add steak; cook until browned, about 7 minutes. Turn. Add onions to pan around steak; cook until meat and onions are browned, about 7 minutes.transfer meat to platter.

To onions in skillet, add 1/3 cup water, vinegar and mustard. Cook over medium heat, scraping up any brown bits. Bring just to boil; cook, stirring occasionally, until slightly thickened. Stir in remaining butter.Pour over steak.