blog/themes/plain/layouts/partials/nav.html

{{ $parent := .Parent }}
<nav class="site-nav">
  {{ if and $parent (not $parent.IsHome) }}
    <a href="{{ $parent.RelPermalink }}">&larr; {{ with $parent.Title }}{{ . }}{{ else }}{{ $parent.Section }}{{ end }}</a>
  {{ else }}
    <a href="/">&larr; home</a>
  {{ end }}
</nav>