Refactoring nested callbacks, node.js, async

function indexArticles(callback) {
  fs.readdir("posts/", function(err, files) {
    async.map(files, readPost, function(err, markdown) {
      async.map(markdown, parse, function(err, results) {
        async.sortBy(results, function(obj, callback) {
          callback(err, obj.date);
        }, function(err, sorted) {
          callback( {"articles": sorted.reverse()} );
        });
      });
    });
  });
}

I'm trying to figure out how to make this prettier -- as you can tell I'm using caolan's async library, but I'm not sure which of the control flow structures to use. It seems like if I use async.waterfall, for example, that results in quite a bit more code, with each step having to be wrapped in an anonymous function. For example, this is just the first two lines of the nested version with waterfall:

function indexArticles(callback) {
  async.waterfall([
    function(callback) {
      fs.readdir("posts/", function(err, files) {
        callback(err, files)
      })
    },

    function(files, callback) {
      async.map(files, readPost, function(err, markdown) {
        callback(err, markdown)
      })
    }])
}

How would you improve this?

If there were a way to partially apply arguments NOT only from the left, then I could see doing, for example,

function indexArticles(callback) {
  async.waterfall([
    async.apply(fs.readdir, "posts/"),
    async.apply(async.map, __, readPost),
    async.apply(async.map, __, parse),
    // etc...
  ])
}