Preheat oven to 450°F.
For the Chips, slice potatoes1/8 inch thick or use the ruffled slicer on a mandolin for wavy fries. Place them on a baking sheet, spray lightly with natural olive oil spray, season with salt and pepper, and arrange the potatoes in single layer. Roast chips 25-30 minutes turning once. After removing from the oven, toss with parsley, chives, cheese and truffle oil.
While the chips cook, dress steak with olive oil and season with salt and pepper.
Preheat a cast-iron pan, griddle or grill to medium-high. Grill meat 10-12 minutes, turning occasionally, for medium-rare to medium doneness; let rest.
Heat olive oil, 2 turns of the pan, in a skillet with a tight-fitting lid. Add bacon or pancetta, and render 2 minutes. Add leeks and garlic, stir a minute, then add tomatoes and season with a little salt and black pepper. Cover pan with the lid to slump tomatoes, 10-12 minutes, shaking pan occasionally. Add balsamic vinegar and remove from heat.
Slice steak across the grain 1/4-inch thick; top with BLT sauce.