Method 1
This approach essentially disables automatic summary splitting on your site. In your site configuration:
summaryLength = 999999 # Tolstoy's War and Peace has around 600000 words.
Then in your template you can do:
{{ .Summary }}
This will return a stripped version of .Content
unless you (a) manually split the summary with the <!--more-->
tag, or (b) define the summary in front matter.
Method 2 (recommended)
Parse the raw content for the <!--more-->
tag.
{{ if or (findRE `<!--more-->` .RawContent) .Params.Summary }}
{{ .Summary }}
{{ else }}
{{ .Content }}
{{ end }}
This will return .Content
unless you (a) manually split the summary with the <!--more-->
tag, or (b) define the summary in front matter.