At any rate, this quest will likely fall into your queue at the same time as Leif's Jade Owl Antidote quest, which is fortunate, since the two quests actually share two line items - the Ice Rune Potion and the trip to Frost Owl Spire.
Once you have completed this quest (and possibly have attained Level 42), Magnus will give you his Cold Comfort quest.
Concoct 1 Ice Rune Potion
Put together 1 Feathered Charm
Send Magnus back to the Frost Owl Spire