blog/.themes/classic/source/_includes/asides/recent_posts.html

<section>
  <h1>Recent Posts</h1>
  <ul id="recent_posts">
    {% for post in site.posts limit: site.recent_posts %}
      <li class="post">
        <a href="{{ root_url }}{{ post.url }}">{{ post.title }}</a>
      </li>
    {% endfor %}
  </ul>
</section>