Chef's Hat
Sold by Burgy Blackheart. Just to save a bit of clicking as no one has said it here yet. This is brought from cooking vendors in Dalaran in Northrend, it is not available from the vendors in Legion's Dalaran.
The 
Chef's Hat is a toy purchased from cooking vendors in Dalaran (Northrend) using Epicurean's Award, granting a permanent Cooking Speed buff without replacing your helmet slot.
Guide awaiting review
Travel to Northrend Dalaran
From your main city's portal room, travel to Dalaran in Crystalsong Forest. Alliance players should find Derek Odds, and Horde players should find Misensi — both are cooking vendors in Northrend's Dalaran, not Legion's Dalaran.
Purchase with Epicurean's Award
Buy the Chef's Hat for 100 Epicurean's Award. Earn these by completing the Dalaran cooking daily plus a second daily from a major capital city — certain capital quests award 2 Epicurean's Award each. Alliance capital quests that award 2 include Ribs for the Sentinels (Darnassus), Keepin' the Haggis Flowin' (Ironforge), and Feeling Crabby? (Stormwind). Horde equivalents include Everything Is Better with Bacon (Orgrimmar) and Corn Mash (Thunder Bluff). During Wrath of the Lich King Timewalking weeks, you can also exchange Timewarped Badges — 25 
Timewarped Badges per currency from the small spice bag.
Tips
To use the Chef's Hat on a new character, you need Northrend Cooking skill 25. Learn Northrend Cooking from your faction's cooking trainer in Dalaran, Crystalsong Forest, then craft Rhino Dogs using Rhino Meat farmed from rhinos between Warsong Hold and Amber Ledge in Borean Tundra — around 35 pieces of meat will get you to skill 25.
To remove the Chef's Hat appearance and buff, simply right-click the Cooking Speed buff — your actual helmet gear is never replaced.
