Hi Marie Elaine and welcome to the Disney Parks Moms Panel.
As far as I am aware, you can order the Cinderella Glass Slipper Dessert at
Cinderella's Royal Table.
As the Cinderella Glass Slipper Dessert is deemed to be a royal enhancement which you can add on, it will not be covered by your Disney Dining Plan and would therefore need to be paid for out of pocket.
The slipper is available in white or dark chocolate and is filled with chocolate mousse, and surrounded by fresh berries. You can even add a celebratory message to the plate if you'd like.
In order to request the Cinderella Glass Slipper Dessert, I would recommend that you send an email to wdw.crt.special.events@disney.com as stated on the Celebrations for One and All section on the Cinderella's Royal Table page of the Walt Disney World website. I do believe that 48 hours advance notice is required for ordering.
Alternatively, you could call Disney Dining on 0800 16 90 748.
Wishing you a magical trip filled with memories which will last a lifetime!
Emma