Warm Roast Beef Sandwich with Rosemary Roasted Onion and Olives

Ingredients

• 2 medium onions, halved and thinly sliced crosswise
• ¼ cup pitted kalamata olives, halved
• ½ cup Filippo Berio Organic Extra Virgin Olive Oil, divided
• 1 sprig rosemary, leaves removed and chopped
• ½ tsp. granulated sugar
• Kosher salt
• freshly ground black pepper
• 4 large thick slices tomato
• 4 kaiser rolls, with poppy seeds or plain, halved
• 12 large thin slices roast beef (about ¾ lb.)
• 1 Tbs. Dijon mustard
• 2 bs. drained prepared horseradish
• 3 oz. blue cheese, crumbled