[Toadling]

The best way to do this is to "group by completed" in the "completed" perspective (don't recall if the "completed" perspective does this by default). This will break down all your completed items into groupings based on completion date. Collapse the ones you're not interested in.

You can then save these settings as a new perspective or just save them to the built-in "completed" perspective.

Hope this helps.

-Dennis