Wordpress Sidebar - Show posts grouped by month

I have a http://www.coreenergetics.com.br/core domain and my client wants in the sidebar appear the last post grouped by month.

I almost got close, but the months are doubling ... how do I make it: (Month + Posts this month) and not (Month + Posts, Posts month + ...)

The code I'm using is:

<ul>
<? php 
   $ aRecentPosts = new WP_Query ("showposts = 10");
    while (aRecentPosts-> have_posts $ ()): $ aRecentPosts-> the_post ();?> 
         <li> <strong> <? php the_time ('F Y')?> </ strong> </ li>
         <li> <a href="<?php the_permalink() ?> "> <? php the_title ()? a> </ li>
   <? php endwhile; ?>
</ ul>

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