blah.php

<h1><?php echo $the_var ?></h1>

index.tpl

<h1>{$the_var}</h1>

TestController.php

<?php

use \silk\database\Database;

class TestController extends \silk\action\Controller
{
	function index()
	{
		$this->set('the_var', "It works!");
	}

	function blah()
	{
		$this->set('the_var', 'This also works!');
	}
}