torophp_base_class.php

<?php

abstract class BaseHandler {
    protected $templateVariables;

    public function __construct() {
        $this->templateVariables = array(
            'base_url' => BASE_URL
        );
    }
}

class TestHandler extends BaseHandler {
    public function get() {
        $tpl = $this->mustache->loadTemplate('test');

        $this->templateVariables['foo'] = 'bar';

        echo $tpl->render($this->templateVariables);
    }
}