In a small bowl, mix the balsamic vinegar with the salt, pepper and mustard until well combined using a small whisk.
While whisking continuously, add the olive oil to the vinegar in small dribbles, making sure that each dribble of oil is emulsified with the vinegar before adding more oil.
In a large bowl, toss the vinaigrette with the baby arugula until the arugula is coated pretty evenly.
Tear the prosciutto into bite sized pieces and lay over top of dressed arugula.
Using a vegetable peeler, shave as much Parmesan cheese onto the salad as you like. I use approximately 2 ounces.
This serves 2 for a dinner salad or 4 for a generous side salad.