Add your own Twig extensions in Silex

gistfile1.aw

// additional twig extensions
$oldTwigConfiguration = isset($app['twig.configure']) ? $app['twig.configure']: function(){};
$app['twig.configure'] = $app->protect(function($twig) use ($oldTwigConfiguration) {
    $oldTwigConfiguration($twig);
    $twig->addExtension(new Some\Twig\Extension());
});