While setting up a new Middleman Blog project, I ran into an issue with blog posts not rendering form a template with a
wrap_template at the top. After a few hours of digging and checking every line for spelling/syntax, I discovered the issue was that the blog layout was an .erb file and was attempting to wrap layout.HAML. It seems Middleman doesn't handle mixed formats in this situation. Hope that saves someone else a little time and frustration.