title: magento disable proceed to checkout until condition is true
body: <p>What magento method I can use to stop the checkout button to function until a certain condition its true?
  basically is a user has deleted a product on basket while he must not checkout until two products are on the basket </p>
  
  <pre><code>public function deleteAction()
  {
      parent::deleteAction();
  
     if($this-&gt;_getCart()-&gt;getQuote()-&gt;getItemsCount() == 1) {
        $this-&gt;addErrorMessage('Please remove one voucher. Or add one More infant milk product');
      }
      }
  </code></pre>