St. Honoratus (and/or the urn containing his relics) was well-known by 1202. That was the year a baker by the name of Renold Theriens donated a plot of land in Paris so that a chapel might be built in the saint’s honor. Though I haven’t seen anything to back this conjecture up, it seems that this was the time that Honoratus became formally associated with baking.
Frequented by bakers and others drawn to the cult of Honoratus, the chapel become quite a success. So much so that in 1400 the bakers of Paris formally established their guild there. I don’t know what ever became of the chapel, though it seems doubtful it’s still standing. As a Catholic and a baker I’d love to visit and say a prayer there. Cultism certainly isn’t encouraged in the Church these days, but when it comes to projects as complicated as Gâteau St. Honoré, I need all the help I can get.