Scrub the outside of the lemon to remove any waxy coating. Zest the skin of the lemon avoiding any white pith. Juice half the remaining lemon.
Combine the zest, lemon juice, olive oil and rosemary together and set aside.
Trim the asparagus spears, snapping the woody end off with your hand. Wash and steam for 3 minutes. Plunge the spears into cold water to stop further cooking.
Dry roast the pine nuts in a small pan until slightly golden.
To serve drizzle the dressing over the cooked asparagus. Top with pine nuts annd season with black pepper.