Growing up (and into adulthood) I thought "getting your just deserts" was "just dessert"*. So you only got for dessert what your behaviour merited. It still makes complete sense to me.
*And I know I wasn't alone.
The original meaning of "desert" (pronounced exactly as dessert but more often used in plural) is of course "deserved reward or punishment".
With all my reading on ethics now I realize I'm at a crossroads because some say that "deserts" in that sense is obsolete. And dessert is more fun, and inclusive. When do we claim the meaning of a word has retired?
(I'll likely use both.)