Get HTML for a standalone layout in Magento

standalone_layout.php

<?php
/**
 * Retrieve content of a standalone layout
 *
 * @return string
 * @throws Mage_Core_Exception
 */
public function getStandaloneLayoutHtml()
{
    $layout = Mage::getModel('core/layout'); // Instanciate a brand new layout (not using the singleton from Mage::app()->getLayout())
    $layout->setArea('frontend'); // Set the area for the layout (frontend or adminhtml)
    $update = $layout->getUpdate(); // Get the layout update object
    $update->load(array('update_handle_1', 'update_handle_2')); // Load update handles (array | string)
    
    $layout->generateXml();
    $layout->generateBlocks();

    return $layout->getOutput();
}
?>

In some situations, you may want to create a layout based on very specific handles. Using the $layout singleton of the current page is then of no use and may lead to bugs. The solution is to create a new standalone layout object in which you can inject your preferred layout handles.