Butterfly Flank Steak (16 ounce) by laying flat and slicing in half lengthwise with the grain, stopping 1-2 inches before cutting all the way through.
Open up flank steak like a book and place between two pieces of parchment. Pound flat with a mallet to an approximate 12x8-inch rectangle. Try to flatten the seam to the same thickness.
Season the flattened flank steak with Salt (to taste) and Ground Black Pepper (to taste) and brush generously with Dijon Mustard (2 tablespoon).
Cover with Prosciutto (3 slice) slices in an even layer. Arrange Fresh Basil Leaf (18) in a single layer on top of the prosciutto. Top with an even layer of Provolone Cheese Slices (4 slice).
With the prepped steak facing you lengthwise, roll up tightly. Secure with a few toothpicks to hold it while you tie it.
Using butcher string, snugly tie the rolled steak at 1-inch intervals. Remove toothpicks and cut roll evenly between each piece of string, giving you about 8 one-inch rolls tied in the centre with string.
Preheat grill or frying pan to medium-high. Rub or brush prepared rolls on both sides with Oil (1 tablespoon)
Cook for 4-5 minutes per side for medium by grilling directly on the grill, using a mesh grill mat on the grill or by pan-frying.
Allow to rest 2-3 minutes, then slice and serve.