. If you want an ascending order, it'd look like this:
<MTArchiveYear order="ascend">
<MTArchiveYearIfEntries><MTArchiveLoad>
<h3><$MTArchiveDate format="%B"$></h3>
<MTEntries sort_order="ascend">
<a href="<$MTEntryPermalink$>"><$MTEntryTitle$></a><br />
</MTEntries>
</MTArchiveLoad></MTArchiveYearIfEntries>
</MTArchiveYear>
ArchiveLoad is needed to fill in the entries for each month context.