replacing .php ext with .html through .htaccess

Question

Greetings!

I'm trying to replace .php extensions with .html

So far I got:

RewriteRule ^(.*)\.html $1.php

... it works nicely when url like /site/page.html is entered (and page.html does not physically exist but page.php does).

However what I'd like to have is when /site/page.php is entered the viewer sees only /site/page.html in the browser location.

Is that doable or do I have to set up explicit redirects for each page? :-(

Thanks in advance.

ps: dev environment I'm using is XAMPP on os x if it makes any difference