Creamy Balsamic Steak with Onions and Mushrooms

INGREDIENTS

• 1/2 cup PLUS 2 Tbsp. Hellmann's® or Best Foods® Real Mayonnaise, divided
• 1 package (10 oz.) cremini mushrooms, sliced
• 1 large onion, thinly sliced
• 1 clove garlic, finely chopped
• 1/4 cup balsamic vinegar
• 1/4 cup beef broth
• 1/2 tsp. fresh thyme leaves or 1/4 tsp dried thyme
• 1 -lb. boneless sirloin steak