Magister Ladd:
Go to the Lair of Antharas and kill the bloody guardians. For your efforts you will get Blood Fire, the flame of purgatory that burns in their bodies. This is what we will need to mix True Gold and Pure Silver.
Use this mixing stone in conjunction with the mixing urn under the Ivory Tower to combine the three ingredients. Set the temperature to #3 Phoenix.
Mimir's Elixir will be born from that flame.