1) Take the Balsamic vinegar, brown sugar, dijon mustard and the garlic and put in a large ziploc bag. Place the London Broil in the bag and marinate for at least 2 hours.
2) Prepare the grill and then remove the steak from the bag. Season the steak with salt and pepper. Grill 6-7 minutes on each side, or until desired doneness. Move the steak to a cutting board and cut across the grain into thin slices.
3) In a large pot, heat over medium heat and add oinion to cook for 25-30 minutes until caramelized. Stir Frequently. Add the vinegar, sugar, roasted garlic until all the liquid is evaporated.
4) Stir in the basil salt and pepper. The grill the slices of bread, remove from grill and brush with Extra Virgin Olive Oil, spread the roasted garlic over the top of each slice.