Take RER-B direction St. Remy to the Chatelet les Halles station. Transfer to RER A in the direction of either Chessy-Marne la Vallee or Boissy-St. Leger. It's just one stop in either direction.

You could also do the Metro to Chatelet les Halles and switch to RER A. Either way works. There are fewer stops on the RER so it's probably faster. I didn't check times.

You can check schedules and routes at http://www.ratp.fr/

Enjoy your trip. Where are you staying in Burgundy? Lovely countryside!