It took me longer than I’d like to admit to correctly spell just deserts. As a kid, I regulary confused desert (sandy) and dessert (sweet), and I suspect the only reason I never desserted anyone is because I would never voluntarily give up my candy.
Just deserts is a funny phrase. When I see it, I think of North Africa or Arizona: a dry land of just deserts. When I hear it or say it, I imagine a French king sitting at the head of an ornate, wooden table full of cakes, ice cream and other goodies. Here’s an example of ambiguity: is the table full of cakes or the king? It depends on when you ask, before or after the meal. It’s also another ambiguity, because you can’t be sure whether I’m asking if the table or the king is full of cakes, or whether the table is full of food or full of the king? English gives me headaches, and neither of the images relates to the actual meaning of the phrase just deserts, which is used to describe a punishment justly deserved. That’s how I remember the spelling today: what I deserve is my desert(s). The plural is optional but commonly used.
Unfortunately, while that solves the problem of spelling, it raises the question of redundancy. If deserts are what someone deserves, what are just deserts: what someone justly deserves? I think justice is implicit in deserving. It goes without saying that what someone deserves is justly deserved unless stated otherwise. Wouldn’t unjust deserts be the more useful phrase?
Anyhow, I made up a silly story to help me remember all of this:
I ate dinner in the Sahara. Chocolate: just desserts. All around me was sand—just deserts. In the evening I got a stomach ache; such were my just deserts.
Now I’m hungry.