Do the customers always want the same thing?
This trophy is actually easy if you do it on the day that Emily serves churros in her restaurant. Just have 2 churros on your tray at all times.
On the very first day in the first restaurant, just make sure to always have one of the cookie, the cheesecake and the tea on your tray all the time. You can remove them if someone orders something different, but be sure to restock them again. Sooner or later, someone is going to come in and order a combination two of those items, since there's hardly anything else on the menu to choose from at that point.