How to use the PHP template engine in Twig instead of the Twig syntax within Silex 2

In Silex2 I am able to use Twig templates but I want to use the PHP engine of Twig, instead of the Twig syntax. For example this guide describes how to do it for Symfony but not Silex 2.

My Silex index.php looks like:

$app->register(new Silex\Provider\TwigServiceProvider(), array(
    'twig.path' => __DIR__.'/views',
));

$app->get('/', function() use ($app) {
    return $app['twig']->render('index.html.php', array(
        'name' => 'Bob',
    ));
});

My index.html.php looks like:

<p>Welcome to the index <?php echo $view->name; ?></p>

When I run the app in the browser and view the source, I see the literal string <?php echo $view->name; ?> which hasn't been executed.

I suspect there may be a Twig config setting to tell it I want to use the PHP style templates. To clarify, if I use the Twig syntax instead, e.g.:

<p>Welcome to the index {{ name }} </p>

Then it works and I see the name Bob, therefore I know this is not a web server or PHP config problem.

This code didnt work for me:

$app['template'] = function($app) use($settings) {
    $loader = new \Symfony\Component\Templating\Loader\FilesystemLoader([
        BASE_DIR . $settings->templates_path
    ]);
    $nameParser = new \Symfony\Component\Templating\TemplateNameParser();
    $templating = new \Symfony\Component\Templating\PhpEngine($nameParser, $loader);
    return $templating;
};

though, this is didnt work too:

$app->register(new NS\ViewServiceProvider(), [
    'view.path' => BASE_DIR . $settings->templates_path,
]);

ViewServiceProvider:

class ViewServiceProvider implements ServiceProviderInterface
{
    public function register(Container $app)
    {
        $app['view'] = function($app) {
            $engine  = $app['view.engine'];
            $helpers = isset($app['view.helpers']) ? $app['view.helpers'] : array();
            $helpers = array_merge($helpers, $app['view.default_helpers']);
            $engine->setHelpers($helpers);
            return $engine;
        };
        $app['view.engine'] = function($app) {
            return new PhpEngine($app['view.parser'], $app['view.loader']);
        };
        $app['view.loader'] = function($app) {
            $paths = isset($app['view.path']) ? $app['view.path'] : array();
            return new FileSystemLoader($paths);
        };
        $app['view.parser'] = function() {
            return new TemplateNameParser;
        };
        $app['view.default_helpers'] = function() {
            return array(
                new \Symfony\Component\Templating\Helper\SlotsHelper
            );
        };
    }
}

Both throws an error, that cannot find the view.php file