Have not come across a Hadith which explicitly mentions this particular practice.

Rasulullah (sallallahu ‘alayhi wa sallam) and the Sahabah (radiyallahu ‘anhum) did not have the luxury of eating a meal on a daily basis, let alone having a variety of dishes for one meal. Therefore such a practice cannot be deemed a regular or emphasised Sunnah of Nabi (sallallahu ‘alayhi wa sallam).

There are certain instances wherein Nabi (sallallahu ‘alayhi wa sallam) ate dates before a meal. Based on this, having something sweet before a meal could be established. (Sahih Muslim, Hadith: 2038).  However, this is not a regular or emphasized Sunnah or practice of the Holy Prophet Sall-Allahu alayhi wa sallam.

And Allah Ta’ala Knows best

https://hadithanswers.com/eating-something-sweet-before-a-meal/
http://darulihsan.com/index.php/q-a/miscellaneous/item/3448-eating-sweets-before-or-after-a-meal