Oh wow. I (non-native) never realized it only had one s, I always assumed it was "just desserts", as in, you are getting the dessert you deserve, after the food (the evil you did) :D
TWL (Today We Learned)
I always assumed it was one one of those odd manglings that gained traction, like irregardless.
https://www.merriam-webster.com/words-at-play/just-deserts-o...