index.html

<h1>{{title}}</h1>

mustache.express.js

//change express render engine to mustache
var express = require('express'),
    app = express.createServer(),
    port = 1234,
    mustache = require('mustache');

app.register('.html', {
    render: function(str, options){
        return mustache.to_html(str, options.locals);
    }
});

app.set('view engine', 'mustache');
app.set('view options', {
    layout: false
});

app.get('/', function(req, res){
    res.render('index.html', {
        locals: {
            title: 'f2e.us'
        }
    });
});

app.listen(port);

output.sh

[~ dev]$ curl http://localhost:1234
<h1>f2e.us</h1>