Egyptian Walking Onions (Allium cepa) are perennial onions. They are super prolific and if you replant the top bulbils every year you can have a near infinite amount of onions. The bottom bulbs are large enough to cook with, and the tops make excellent green onions.
Sold as bundles of 10 bottom bulbs or 20 top bulbils.
Photo credit: Tony Alter from Newport News, USA, CC BY 2.0 <https://creativecommons.org/licenses/by/2.0>, via Wikimedia Commons