They're Ravenous In Darnassus

If you get to the area and find the tree of Darnassus is burning, you need to go talk to Zidormi at 48.07, 25.67 and have her send you back to the time before Darnassus was destroyed. You will then be able to go into Darnassus and complete the quests. https://www.wowhead.com/npc=141489/zidormi

Associated with the Pilgrim's Bounty, a week-long event introduced in 2009. Here is a little information about the event itself:

Name: Pilgrim's Bounty
Duration: November 8 to November 14 (2009)
Real-world equivalent: Thanksgiving
Official description: Pilgrim's Bounty is time to reflect upon one's good fortune and share with all around you.

Head for the feasting area, just outside Darnasus
(This post assumes that you are continuing the quest sequence (as listed at the top-right of this page).).

No cooking is required.

Hand in your extra:

5 x Spice Bread Stuffing (created during Quest: Spice Bread Stuffing)
5 x Pumpkin Pie (created during Quest: Pumpkin Pie)

at Isaac Allerton, who then gives:
Candied Sweet Potatoes

Before you leave, remember to purchase (at Ikaneba Summerset (outside Darnasus) or at a nearby Bountiful Barrel):
- 25 x Teldrassil Sweet Potato (5 for that quest & 20 more for Daily: She Says Potato (towards Achievement: Pilgrim's Progress))

Head for Stormwind.