How do I recreate the system.site configuration element? For some reason system.site, system.performance and system.date config values have been deleted from our site. 

I have the original configuration files, but when attempting to import those using drush cim, Drush complains about the site UUID mismatch. 

The import failed due to the following reasons:                 
Site UUID in source storage does not match the target storage. 


I assume this is because UUID is missing entirely. If I run drush cget system.site, I get the following error:

[error]  Config system.site does not exist 


Attempting to set the UUID with drush config-set "system.site" uuid "my site id" also fails with:

[error]  Config system.site does not exist 


So now I'm in a bit of conundrum.

Any suggestions on how to restore the system.site configuration?
I solved it with Drush. 

To get around the UUID mismatch I uncommented the UUID field in system.site.yml and ran drush cim. After that I specifically set the UUID by running drush cset "system.site" uuid "my site id".