I am trying to transform all of the web.config files in a project I have, here\'s a my tree structure:
I think you were pretty close. I have pasted a sample below which shows how to do this.
In my sample I discover the transform sitting next to the web.config file itself. For your scenario you can just use an MSBuild property pointing to a specific file.
Release
C:\temp\transformed-files\
FYI you can download a full sample at https://github.com/sayedihashimi/sayed-samples/tree/master/TransformMultipleWebConfigs.