I went to Cordon Bleu in Paris but for the whole program. They used to offer single day classes but check to make sure.
You may try Daniel Rose, chef/owner of Spring. He sometimes does demo classes at the restaurant. He's actually a Chicago area native and his place is one of the hottest in Paris - often compared to Schwa, which it resembles a bit in style.
For serious, hardcore classes, Pierre Herme offers them but for professional pastry chefs only.
Overall I recommend the awesome Paule Caillat at Promendades Gourmandes. I first met Paule at a party at Dorie Greenspan's home. Between them, they know everything and everybody there is to know about food in Paris.
http://www.promenadesgourmandes.com/