How to add a WiX custom action that happens only on uninstall (via MSI)?

I understand the RemoveFile and RemoveFolder options in WiX, but these are not robust enough to recursively delete an entire folder that has content created after the installation.

I noticed the similar Stack Overflow question Removing files when uninstalling WiX, but I was wondering if this could be done more simply using a call to a batch script to delete the folder. This is my first time using WiX, and I'm still getting the hang of custom actions. What would be a basic example of a custom action that will run a batch script on uninstall?