Aha, and this is how Rachel gets exposed.
Rael's already suspicious Rachel was lying about the dress and pretty sure Marie designed it. He didn't get a direct answer from Marie if she designed the dress, so he sent away the patisserie to force Rachel to bake cookies. He knows Rachel probably can't bake cookies, but if the cookies she produces taste like Marie's (since Rael knows what Marie's cookies taste like), then he can confirm that Marie helped Rachel bake cookies and certainly made her dress.
Sneaky Rael. Marie, it's a trap!