1. In between plastic wrap, pound out the flank steak to tenderize it. slice the steak, against the grain and at a sharp angle, into thin strips.
1a. In a small bowl, whisk together 2 tablespoons of olive oil, balsamic vinegar, brown sugar and garlic. Put the steak into a zip-top bag with the marinade and let sit for 1 hour in the refrigerator.
2. In a small bowl mash the blue cheese and buttermilk with a fork until creamy. Stir in the Worcestershire sauce and set aside.
3. In a large skillet heat the remaining olive oil and toss in the red onion. Cook until caramelized and remove to a plate. In the same skillet cook the flank steak strips seasoning it with salt and pepper. About 3 minutes per side.
4. To serve, place a couple of strips of steak on a lettuce leaf. Top with the onions and blue cheese dressing. Makes 4 servings - 3 wraps per person.