Here is an early chance to get this one - this is how I did it.
During the Quest 'Lilac & Gooseberries', after your fight with the Griffin, you meet your colleague back in the White Orchard tavern.
After a cut-scene you are set upon by some guys in the tavern - and it is here that I unlocked this.
During the quest I had earnt extra ability points by doing side-quests and fighting low-level enemies (drowners, wolves etc), and finding a few Places of Power.
I put an Ability Point into the "Fireball" Sign (cannot remember the name), and come this fight the extra power, plus their close vicinity, meant once I had used that and swung my sword a few times I had easily defeated them all.