1. Combine butter, garlic, parsley, lemon zest, 1/4 tsp. salt and pepper in a food processor. Process until blended, stopping and scraping the sides as necessary. Use immediately or scrape butter onto plastic wrap, shape into a log and wrap tightly; store up to 1 week in the refrigerator or 2 months in the freezer.
2. Place asparagus in a large skillet so it lies flat. Add cold water to cover, plus a pinch of salt. Bring to a boil over high heat; reduce heat to medium-low and simmer until tender, 5 to 10 minutes. Drain well, pat dry and transfer to a platter. Add some herbed butter and serve warm.