Can I cook the tops of bulb onions that have begun to grow?

You could use the shoots. they would have a milder onion flavor.

I get that a lot. They cook up just fine.

Yes, I do all the time BUT… First cut off the root and then split the bulb. Discard any layers that are translucent, brown, or soft. The firm white layers and the green and white shoot are fine to use, just like spring onions; rinse before using. As the onion shoot starts to grow it “steals” food from layers, and those layers start to rot. They will smell and taste bad if you use them.

I use them all the time when looking for a light onion taste they cook up just wonderfully.

Thanks folks. They tasted great.