blog/_src/_includes/featured.html

<aside class="featured">
    <div class="grid grid--gutters">
        {% for post in site.posts %}
            {% if post.featured %}
            <article class="grid__col">
                <a class="featured-link" href="{{ post.url }}" title="{{ post.title }}">
                    {% picture featured {{ post.image }} %}
                    <h1 class="featured-title">{{ post.title | titlecase }}</h1>
                </a>
            </article>
            {% endif %}
        {% endfor %}
    </div>
</aside>