how to add if/else statement to base.html?

I'm trying to put the if/else statement to my base.html file. The idea is to have if/else as a part of the template that will be an extension for my HTML files. The problem is, I'm not sure what syntax would look like.

Previously, I had an HTML page (called the essay-page) with some content and if/else statement hardcoded to this particular page. But I want to have if/else as a part of my template too, so I could use it with several pages.

Essay-page with hardcoded if/else:

{% block body %}

{% if essay_found %}

<article>
    <img src="" alt="">

    <section id="location">
        <h2>Other infos</h2>
        <address>This essay was made in <span>LOCATION</span> (ADDRESS).</address>
    </section>

    <section id="details">
        <h2>What's this essay about?</h2>
        <p>{{ essay_description }}</p>
        <footer>
            <p>Need more details? <a href="">Please contact me</a> (but don't spam ;))</p>
        </footer>
    </section>
    <section id="registration">
        <h2>Send me your request and job offers!</h2>
        FORM
    </section>
</article>

{% else %}
<h2>No essay found for this slug, sorry! </h2>
{% endif %}

{% endblock%}

now I try to put this if/else to my base.html (without a success):

<main>
    {% block body %}

        {% if essay_found %}

        {% block article %}{% endblock %}

        {% else %}
        <h2>No essay found for this slug, sorry! </h2>
        {% endif %}

    {% endblock %}
    </main>

and update essay-page to:

{% block body %}


{% block article%}
<article>
    <img src="" alt="">

    <section id="location">
        <h2>Other infos</h2>
        <address>This essay was made in <span>LOCATION</span> (ADDRESS).</address>
    </section>

    <section id="details">
        <h2>What's this essay about?</h2>
        <p>{{ essay_description }}</p>
        <footer>
            <p>Need more details? <a href="">Please contact me</a> (but don't spam ;))</p>
        </footer>
    </section>
    <section id="registration">
        <h2>Send me your request and job offers!</h2>
        FORM
    </section>
</article>
{% endblock %}

{% endblock%}

I'm not sure if the problem is related to the lack of super block on the essay-page (because the blocks would be nested), or the syntax of if/else statement in base.html.