I originally titled this post ‘Just ‘desserts” but I decided it would seem like I was trying to be clever.
Anyway, I expect that the misuse of either of these words is down to not knowing how many s’s to spell it with. The meanings are as follows:
Desert: Wastelands or a barren area of land; to abandon somebody or something (including military duties without leave); or to get what you deserve/be treated as you deserve (e.g. ‘just deserts’).
If it is a sweet food then use two s’s. If it is any of the other options, just use the one s.