In a bowl, mix together vinegar, oil, rosemary, garlic, lemon juice and salt and pepper blend. Put the steak in an 8 by 12-inch casserole dish and generously coat with the vinegar mixture. Allow to marinate for 30 minutes to 1 hour in the refrigerator.
Preheat an outdoor grill or indoor grill pan.
Remove the steak from the marinade, straining excess marinade from the steak. Removing the excess marinade will prevent flaming, or charring of the steak during cooking. Put the steak on the grill, and cook over high heat, about 8 to 9 minutes per side. Remove the steak from the grill to a cutting board and let rest, about 5 minutes, before cutting. Slice the steak on the bias, top to bottom, against the grain, 1/4-inch thick. Arrange the steak over the potatoes on a serving platter and serve.
Preheat oven to 400 degrees F.
In a large bowl, mix together the oil, 1 teaspoon of parsley, the garlic, onion, and salt and pepper blend. Add the potatoes and toss to coat. Transfer the seasoned potatoes onto a baking sheet and roast until the onions are soft to touch, about 20 minutes. Remove the potatoes from the oven and set aside. In a large bowl combine the truffle oil, cheese, remaining parsley and thyme. Add potatoes and toss to coat evenly. Return the potatoes to the baking sheet and roast for additional 20 minutes.