Mustache template string inside render as HTML

From the Mustache documentation:

All variables are HTML escaped by default. If you want to return
unescaped HTML, use the triple mustache: {{{name}}}.

So you just have to use eg.{{{content}}} in your template:

  <div id="box">
    <div id="title"> {{title}} </div> 
    <div id="content"> {{{content}}} </div> 
    <div id="footer"> {{footer}} </div> 
  </div>