There is an old expression: he got his just deserts. It is spelled with one S in the middle. However, if you are setting up a banquet hall, and you want a table reserved for just desserts, you would spell that with a double S in the middle. I always remember that dessert has two Ss because I will want two servings of it.
Just deserts—what you justly deserve, usually used in relation to punishment.
Just desserts—a selection of only sweet treats and nothing else.
If you want to talk about an unpopulated island where someone might be stranded—the setting of many hypothetical questions—you could call it a desert isle (as was the case with the uncharted one that Gilligan landed on), or a deserted isle. The first means dry and barren; the second means abandoned, so probably still pretty barren. If you saw the Monday Muddle on April 5, you will know that a deserted aisle is what you might find in a grocery store on a slow day. The dessert aisle is less likely to be deserted.
