How to use Caldesann's Despair Kanai's Cube Recipe

How to use the new Cube recipe Caldesann's Despair to add a permanent additional stat to ANY Ancient item:

1: Have an ancient item. Any will do. Best to use one you actually want to wear.

2: Have plenty Flawless Royal Gems crafted. Amethyst for Vitality, Emerald for Dexterity, Ruby...