I have chronically cold hands (to the point that they're painful and interfere with typing), and in the last few years I've discovered that hands down the best way to warm my hands up is to warm my core up more. I have a big down puffer vest that I keep in my office and it's a lifesaver.

This works even when my hands are the only part of my body that feel cold. The body is effectively prioritizing keeping my core warm instead of the extremities, so adding insulation to the body has the trickle-down effect of warming the hands. On the other hand, trying to warm just the hands never feels like enough.