Marinate the steak: In a zip-lock bag or mixing bowel, add balsamic vinegar, honey, soy sauce, Worcestershire sauce, garlic, 1 tablespoon of olive oil, and mustard. Mix well.
Add top round steak to the bag, close the bag and coat the meat thoroughly. Let it marinate for 30 minutes to 2 hours in the refrigerator.
Sous Vide the steak: In the meantime, add water to the sous vide container or a large pot, set the Sous Vide Precision Cooker to 133°F (56°C).
Remove the steak from the marinade and place it in a new zip-lock bag (discard the marinade).
Seal all but one corner of the bag, and slowly place it in the water bath. Make sure everything below the zip-line is covered by water. Then seal the rest of the bag.
Keep the bag in the sous vide container. Make sure the steak is fully submerged while the seams of the bag is above the water.
Cover with several pieces of aluminum foil and sous vide cook for 6-8 hours.
Sear the steak: When your steak is cooked in the sous vide machine, remove the bag from the water bath and transfer it to an ice bath or refrigerator. Let it chill for about 10 minutes.
Remove the steak from the ziplock bag and wipe off the moisture with paper towels.
Season with more salt and pepper if necessary. Brush the steak with oil.
Place the cast-iron skillet or grill on medium-high heat. Once very hot, add the steak and sear about 1-2 minutes per side.
Slice against the grain and serve with potatoes and veggies.