Not too sure what you mean by "fancy schmancy" -- the restaurant atmosphere or the chef's creativity?
My two all-time favorite mashed potatoes are unfortunately no longer around...
No. 1 being
Houston's that was on North Rush Street.
No. 2 being
The Mashed Potato Club that was on W. Erie.
However, I do remember being very impressed with
Red Light's mashed potatos... I think they were Wasabi-Mashed Potatos with a Teriyaki gravy. It was loaded, too: when you took a bite you could feel the burn in the back of your head... Good stuff! Most would say "fancy", but better than settling for Kentucky Fried... (Though if I had to settle for KFC or Popeye's, I'd go with Popeye's mashed potatoes.)
Red Light
820 W. Randolph St.
312-733-8880
http://www.redlight-chicago.com
~GS
Greasy Spoon