fancy-callout.php

<?php
if (!empty($title)) {
?>
<h4>
<?php 
    echo $title; 
?>
</h4>
<?php
}
if (!empty($text)) {
?>
<div class="callout-text">
<?php 
    echo $text; 
?>
</div>
<?php
}

shortcodes.php

<?php
// usage: [fancy-callout heading="Custom Heading"]Custom Content[/fancy-callout]
add_shortcode('fancy-callout', function ($atts, $content = null) {
    return silencio_partial('fancy-callout', ['heading' => $atts['heading'], 'text' => $content], false);
});

single.php

<?php
// .. other single.php logic

silencio_partial('fancy-callout', ['heading' => $post->post_title, 'text' => $post->post_excerpt]);

// .. other single.php logic