Unlocking the quest
The quest can be unlocked during your first visit to [The Cauldron], in the main quest [The Fire of the Mountain]. The quest giver is Karn, and since he's right at the entrance to The Cauldron, you can't miss him. Talk to him after defeating Constructs, and select Favor. Karn will ask you to find a Silver Platter in The Cauldron.
[TIP: Make sure to select the proper dialogue option, because the conversation with Karn is also required to move another side quest - [Shaman's Craft]].
Find Karn's Silver Platter
The item you're looking for is a Silver Platter and you can find it during a first visit to [The Cauldron], in the main quest [The Fire of the Mountain]. In the final stage of the exploration (the second level) you'll be forced to throw a shadowbomb at a switch in order to lower a drawbridge. Go across it and explore the area on the left - you'll stumble upon the platter.
Hand the Platter to Karn
You can now return to Karn, who's standing in the same place as before, at the entrance to the Cauldron (only after completing the main quest connected with this location). Trigger a conversation and select I've found it... The rewards are: 165 XP and 900 gold.