How to make custom error pages work in ASP.NET MVC 4

My current setup (on MVC3, but I think it still applies) relies on having an ErrorController, so I use:

<system.web>
    <customErrors mode="On" defaultRedirect="~/Error">
      <error redirect="~/Error/NotFound" statusCode="404" />
    </customErrors>
</system.web>

And the controller contains the following:

public class ErrorController : Controller
{
    public ViewResult Index()
    {
        return View("Error");
    }
    public ViewResult NotFound()
    {
        Response.StatusCode = 404;  //you may want to set this to 200
        return View("NotFound");
    }
}

And the views just the way you implement them. I tend to add a bit of logic though, to show the stack trace and error information if the application is in debug mode. So Error.cshtml looks something like this:

@model System.Web.Mvc.HandleErrorInfo
@{
    Layout = "_Layout.cshtml";
    ViewBag.Title = "Error";
}
<div class="list-header clearfix">
    <span>Error</span>
</div>
<div class="list-sfs-holder">
    <div class="alert alert-error">
        An unexpected error has occurred. Please contact the system administrator.
    </div>
    @if (Model != null && HttpContext.Current.IsDebuggingEnabled)
    {
        <div>
            <p>
                <b>Exception:</b> @Model.Exception.Message<br />
                <b>Controller:</b> @Model.ControllerName<br />
                <b>Action:</b> @Model.ActionName
            </p>
            <div style="overflow:scroll">
                <pre>
                    @Model.Exception.StackTrace
                </pre>
            </div>
        </div>
    }
</div>