To my considerable relief, the nod of the Nodding Onion is distinctive, and I can assert with some confidence that this is Allium cernuum.
And since I have not yet had occasion to use the word “umbel”–and who wouldn’t want to use the word?–I will add this note: an umbel is a form in which flower stalks radiate from a common point. The shape is often described as an inverted or upside-down umbrella, with the ribs pointing up, but thanks to the characteristic nod, the umbrella in this species is right-side-up.
Although, looking from overhead, the umbel might also be likened to a UFO.