Preheat the oven to 425°F and line a sheet pan with parchment, or set a wire rack inside the pan.
Pat the trimmed asparagus completely dry with a towel and toss lightly with olive oil.
Wrap each spear with a half-slice of prosciutto in a loose spiral, leaving the tip exposed, and place seam-side down on the pan with space between each bundle.
Roast for 12 to 15 minutes, until the prosciutto is crisp and the asparagus is tender with a slight bend.
Season with black pepper and serve right away, with balsamic reduction or a squeeze of lemon if desired.
Notes
Do not crowd the pan. Crowded spears trap steam and the prosciutto stays soft instead of crisping.