Just a thought...
I'm not sure I would have used book.xlt. This is the template file that excel
uses whenever you click on that New icon on the standard toolbar (and the
template that is used when excel starts up).
It'll do what you want, but each workbook that is created that is based on this
template file will have that macro in it. That means whenever you open one of
those files, the first file on that MRU list will be opened.
And if you share any of these workbooks with others, then those users will get
that macro, too.
I think I'd either put it in my Personal.xls file (also stored in XLStart) or a
dedicated workbook (Named OpenMRU.xls (?)) stored in that same XLStart folder.
If you use the dedicated workbook, you could modify Dana's code so that the
workbook closes itself, too:
Sub Aut

pen()
Application.RecentFiles(1).Open
Thisworkbook.close savechanges:=false
End Sub