Could you please tell me what was the very first verse to be written down with evidence?

Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

The first verse that was revealed to Prophet Muhammad (Sallallahu Alaihi wa Sallam) was the first verse of Surah Al-‘Alaq (the clot) [96].  Allah Says (interpretation of meaning): {Read! In the Name of your Lord, Who has created (all that exists)}[96:1].

As for the verse that was written first we, do not know it.

Allah knows best.