How to, ultra simple plain text edit for single page, single user.

I need to allow a single user to edit the plain text of the content of a single page, with just a simple form textarea.

I want to avoid all the complexity of the admin environment, just get the actual content into a textarea and the option to modify it and save the new text with a button. The edit script will be hardwired to the specific page.

I administrate the server, so I can modify everything.

Any indication on how to do this?

Thanks!