Buying good-quality rocket is not easy: supermarkets tend to sell it in small packets as a herb, and it is normally limp. Ask your greengrocer to get you some or, better still, grow it yourself. Every time you cut it, it grows again and becomes hotter.
Whisk together the olive oil and balsamic vinegar and season. Lightly toss the rocket leaves with the dressing. Then, with a peeler or sharp knife, shave the Parmesan on to the salad.