More for posterity, this was the last step that was eluding me. I had found numerous resources to get me started on the path to setting up Apache and SSL, but when it came to having a working config and server, when I went to browse my Debian test server, I would get this message:

When you google for the solution I found a number of dead ends, but in the comments for one of them there was a helpful pointer.

When you do an 'ls -la' on sites-enabled (inside /etc/apache2), you will see a symbolic link to the sites-available folder and typically just for the default site (000-default -> default). However in sites-available there's also a default-ssl config file. Creating a symbolic link to this file and reloading apache fixed my problem and now I have apache serving up http over SSL .