htaccess directing all http traffic to https://www.

Hi,

I'm trying to redirect all https://mydomain.com traffic to https://www.mydomain.com

Currently I have:

RewriteCond %{HTTP_HOST} ^mydomain\.com$ [NC]
RewriteRule ^(.*)$ https://www.mydomain.com/$1 [L,R=301]

This directs all http traffic but not https:// (ie without the www).

Any ideas?

Many thanks