This sounds cool as hell:
We took Mikkellers imperial stout Black and distilled it at Braunstein distillery. The alcohol we got out of it was storaged in American bourbon casks. Now distilled Black was poured into bottles, and as soon as the bourbon cask was empty we filled it again, but this time with our imperial stout Black.
In this way, one can say that Black has been barrel aged on itself.
Check out the rest of the release here.