To a small bowl add the cheese, olive oil, vinegar, a pinch of salt and a few cracks of pepper. Whip with a whisk to create a creamy dressing. Taste and adjust salt as needed.
To make the salad:
Toss the butter lettuce in the dressing or drizzle it as you create layers.
Layer leaves of butter lettuce with prosciutto, dressing, and top with peas, reserving extra peas for the top.