Before it closed you could order a slice from Starring Rolls but now that is a thing of the past.
I have found that the recipe in Cooking with Mickey and the Disney Chefs is spot on with just some adjustments.
In a small saucepan take ruby red grapefruit juice (I like to use canned grapefruit slices for the recipe so I save the juice for this step) and sugar and boil it down to a simple syrup (measurement is 1 to 1). Once the cakes have cooled paint the layers with the syrup then add slices of grapefruit and the icing. Voila just like (though not as pretty with the multiple layers and candied grapefruit slice) the one served at the Hollywood Brown Derby