I know this thread is about Madison bars serving T&J's, but if you're in the Chicago Loop, maybe doing Marshall Field's windows (I still call it that) or Millenium Park or Art Institute, stop at Miller's Pub on S. Wabash, next to the Palmer House Hilton. They serve up good home-made Tom and Jerry's, with the mix in a big bowl on the bar. At least they used to. And a great "old time" Chicago "pub" and supper club type place. Throwback place, lots of celebrity photos on the walls, celebs like Jerry Lewis and Bob Hope, etc.
From their web site:
TOM & JERRY – $8
A Holiday Tradition at Miller's Pub since the 1930s. Featured in Esquire, Playboy, GQ, and Chicago Magazine. A variant of eggnog with brandy, Myer's dark rum, powdered sugar, egg whites, vanilla, cinnamon, and nutmeg. "Your Holiday Season will not be complete without trying at least one Tom & Jerry!"