Jekyll Liquid template snippet to list blog items grouped by year and month

blog-summary.liquid

<section class="blog-summary">
{% assign postsByYear = site.posts | group_by_exp:"post", "post.date | date: '%Y'" %}
    {% for year in postsByYear %}
        <h3>{{ year.name }}</h3>
            {% assign postsByMonth = year.items | group_by_exp:"post", "post.date | date: '%B'" %}

            {% for month in postsByMonth %}
                <div class="blog-summary-month">
                    <h4>{{ month.name }}</h4>
                    <ol class="blog-post-list">
                    {% for post in month.items %}
                        <li>
                            <p class="blog-title"><a href="{{ post.url }}">{{ post.title }}</a></p>
                            {% assign author = post.author %}
                            {% assign author_info = site.data.authors[author] %}
                            <time datetime="{{ post.date | date: "%Y-%m-%d" }}">{{ post.date | date: "%-d %b %Y" | trim }}</time>, by {{ author_info['name'] }}
                        </li>
                    {% endfor %}
                    </ol>
                </div>
    {% endfor %}
{% endfor %}
</section>

Note: the author information in my example is loaded from site.data.authors