Remove the London broil from the packaging and pat dry with a paper towel.
Use a fork to pierce the roast. This will allow the marinade to penetrate and add flavor to the beef.
Add the balsamic vinegar, olive oil, and Worcestershire to a small bowl. Whisk together to combine the marinade.
Place the beef in a ziploc bag or container.
Add the marinade to the bag and seal. Place it in the refrigerator for at least 2 hours to marinate. Overnight is best.
Remove the London broil from the refrigerator half an hour before cooking to allow it to come to room temperature.
Remove the London broil from the marinade allowing any excess marinade to drip off.
Place the beef on a wire rack and pat it dry on all sides with a paper towel.
Discard the remaining marinade.
Add the salt, black pepper, fresh thyme, and garlic to a small bowl. Stir together to combine the seasoning mixture.
Spread the seasoning mixture on both sides of the meat.
Place an oven rack on the highest shelf of the oven and preheat your oven to 500 degrees (or broil).
When your oven is preheated, place the London broil on the top rack and cook for 7 minutes.
After 7 minutes flip the beef to the other side and cook for an additional 7 minutes.
London broil is best cooked to a medium-rare temperature of 125 degrees. The more well-done it cooks the tougher it will become.If you desire a more well-done steak, cook it to your desired temperature. Keep in mind the beef will continue to cook and rise 4-7 degrees while it's resting. Tent the beef with aluminum foil and let it rest for 15 minutes before slicing to allow time for the juices to redistribute.
Slice the roast against the grain into ¼-inch thick slices. Serve with your favorite vegetables and compound butter (or melted butter).