title: Call Mixin method when overriding
body: <p>I've got a Mixin in my controller that has a particular action. I need to override this action, do some stuff, and then call the original action provided by the Mixin.</p>
  
  <p>How can I do this?</p>
  
  <p><code>this._super()</code> doesn't seem to work in this case (which does make sense, as it's meant to call the superclass' implementation, not a Mixin's).</p>