Can a single course be recovered without "recovering" the other courses? If so, a how-to would be greatly appreciated.
I believe all you need is the course directory, and any database tables that start with this course name.
If the course was properly deleted, there should be no directory called '/opt/webwork/courses/[coursename]' (assuming you used the default installation path), so copy this directory from your backup. Depending on which user you use to copy the files, you may need to fix the permissions. Easiest way to do this is to follow the instructions in the installation documentation.
For the database tables, it depends how your database was backed up. If you run the following command in mysql on the backup database, it will tell you which tables should be copied:
mysql> show tables like '[coursename]_%';
If you tell me what form your backup is in, I can probably provide more detailed instructions.