If you use middleman and the nice template solution slim you might encounter the same need as I did: appending your site name at the end of your page titles without hardcoding it everywhere.

I found a simple solution, in my layout I added:

    - if current_page.data.title?
        title= current_page.data.title + " | My Website"
    - else
        title My Website

When in your slim pages you have :

---
title: My page title
---

You end up in your generated code using middleman with the title

<title>My page title | My Website</title>

And if the page has no title it will default to :

<title>My Website</title>

This was found when trying to improve diesel documentation.

I hope this can be useful to somebody else.