Break off the woody end of one piece of asparagus; use that as a guide to tell where to trim the other pieces. Then cut asparagus into 2 inch pieces.
Cut each large garlic clove into 3-4 slices. Put asparagus, garlic, and olive oil into large ziploc bag, shake, and let marinate 1-2 hours. (You can skip this step, but the asparagus will be more garlicy tasting if you marinate it.)
Preheat oven to 450 F. Place asparagus on large cookie sheet and season with fresh ground black pepper and salt. Roast until asparagus is slightly softened and edges are starting to brown slightly, about 20 minutes. Serve hot.