The Immortality Potion for Glaucus

Goddess circe met glaucus on a beach and the two hit it off immediately. Glaucus was in awe of circe's beauty and wisdom, and circe found the attention rather flattering. The pair continued to meet every day for months before glaucus asked her if she could turn him into an immortal. She had never considered the possibility of turning glaucus into an immortal; she doubted she would be strong enough to do it. Circy worked around the clock to make an immortality potion but couldn't come up with one that didn't already give people eternal life. Finally after decades of experience under her belt, she realized: There has to be a magical herb that already has immortality