Filet Mignon Skewers with Balsamic Reduction

INGREDIENTS

• 2 Tbs. unsalted butter, plus 1/2 tsp. if reheating
• 2 Tbs. minced shallots
• 1 1/2 tsp. sea salt
• 1 1/2 tsp. freshly ground pepper
• 1 cup medium-bodied fruity red wine, such as Pinot Noir
• 2 Tbs. balsamic vinegar
• 2 lb. filet mignon, trimmed of fat
• Fresh rosemary sprigs for garnish (optional)