Jekyll Kramdown T.O.C. not building - jekyll

Question

Here's the final output of what I'd like to have:
<article itemscope itemtype="http://schema.org/BlogPosting">
<header>
<h1>Jekyll Table of Contents with Kramdown
</h1>
</header>
<nav aria-label="Table of Contents">
<ul>
<li>Topic 1</li>
<li>Topic 2</li>
<li>Topic 3</li>
</ul>
<nav>
<section itemprop="articleBody">
<p>the main body of the article</p>
</section>
</article>
With a default Jekyll install Kramdown can create a TOC with
* TOC
{:toc}
However Markdown is not currently supported in HTML includes or Layout files.
I tried using [Capture and Markdownify}(https://github.com/jekyll/jekyll/issues/6166#issuecomment-322771527) to add the above TOC call to the layout file without success
// _layouts/post.html
<article>
<header>
<h1>Jekyll Table of Contents with Kramdown
</h1>
</header>
{% capture toc %}{% include toc.md %}{% endcapture %}
{{ toc | markdownify }}
<section itemprop="articleBody">
<p>the main body of the article</p>
</section>
</article>
Adding a inline markdownify works for plain markdown but not the Kramdown TOC call.
// this works
{% capture md %}
## Heading 2
*Stuff added in my layout*
{% endcapture %}
{{ md | markdownify }}
// This doesn't work
{% capture md %}
* TOC
{:toc}
{% endcapture %}
{{ md | markdownify }}
The only way I see around this is to include some of the layout markup in the post's markdown file.
// _layouts/post.html
<article>
<header>
<h1>Jekyll Table of Contents with Kramdown
</h1>
</header>
{{ content }}
</article>
// _posts/post.md
---
layout: post
---
<nav aria-label="Table of Contents">
* TOC
{:toc}
</nav>
<section itemprop="articleBody">
## My Heading
Standard markdown content here
</section>
The draw back here is that I've now got page markup in my post that can be easily corrupted and a distraction to content editors.
Does anybody see a way round this?

Answer 1

I found this excellent Ruby Gem jekyll-toc — it generates a TOC that you can place anywhere in your layout files.
I'm now successfully using the following in my _layouts/post.html:
<nav aria-label="Table of Contents">
{{ content | toc_only }}
</nav>
<section itemprop="articleBody">
{{ content }}
</section>