Count and order by relation with Laravel and Eloquent

How can I use Eloquent to count the number of comments from a post and order the posts by number of comments?

My code is something like this:

class Post extends Model
{
    protected $table = 'posts';

    public function comments()
    {
        return $this->hasMany('App\Comment');
    }
}

I need to retrieve a collection of posts ordered by number of comments in an elegant way, thus I would prefer not to use something like DB::select(select count(comment.post_id), post.id from posts left join comments on posts.id = comments.post_id group by post.id order by count(post.id));