Steak Au Poivre Salad - Ellie Krieger

Ingredients

• 2 medium russet potatoes (1 pound)
• 2 medium onions
• 2 cloves garlic
• 1 teaspoon fresh rosemary leaves
• 3 tablespoons extra-virgin olive oil
• 3 tablespoons red wine vinegar
• 1 teaspoon Dijon mustard
• ½ teaspoon coarsely cracked black peppercorns
• ½ teaspoon salt
• Cooking spray
• 1 ¼ pounds sirloin steak
• 2 large hearts of romaine lettuce (¾ pound)
• 3 medium tomatoes