Cut the beefsteak in two equal pieces and wrap the pieces in plastic wraps. Pound the pieces with a meat mallet from center out to the edge until thin. Lift the plastic wrap from time to time, and loosely rewrap the pieces.
Spread the mustard evenly on two, preferably chilled plates, and put the thinly pounded beefsteak slices on them.
Spread the truffle pesto evenly on the beef carpaccio and decorate with some fresh, crisp rucola salad and shaved parmesan cheese.