I think the second time you talke to Jean Michel, he treated you to anything on the menu already.
Then later you go back to him and ordered again to get mint.
Now you want to ask him about the picture in the magazine. He should make a trade if you prepare parfait.
To get this, Nancy should have seen or read the magazine in Minette's office.
Walkthrough: The article on Minette written by Jean Michel Traquenard shows a picture of Minette in this office. Check-click the picture of Carol, the dress form and also see a cut off picture of Minette by the large gears.
Then read the red book from the the secret room.
Walkthrough: See a picture of M380 with a code under the picture. Click on the picture and Nancy will make a comment that it is similar to the paint covered gears in Minette's workroom.