I don't remember the name of the place so this may not be particularly helpful, best I can do is describe where it is. If you are walking away from Place Saint Michel and towards Notre Dame on the road next to the river, past all the tourist shops and come to the first cross roads by the bridge, the restaurant on this corner (ring any bells for anyone?)
Charged 7euros for mulled wine, which was just cheap red warmed up (probably microwaved), and given packets of sugar and a shaker of cinnamon to go with it!