You can! Here’s how to do it:
https://www.happy-mothering.com/how-to-regrow-a-sprouted-onion-in-your-garden/
NOTE: Why can’t I just plant a whole onion?
I have tried planting whole onions, and I find that they have a higher tendency to rot in garden soil compared to planting just the sprout. I don’t recommend it.
Thank you for these tips! We’ll see what I can come up with.