Grand Master Cook
You'll need at least 350 Cooking Skill to train up the last rank, but as soon as you do, achievement -- simple as that.
The Cake Is Not A Lie
For better or for worse, getting the Delicious Chocolate Cake recipe is pure RNG (and until recently a buddy couldn't complete the meta purely because she hadn't gotten it to drop after more than a year). It's a random reward from any of the Outland or Northrend Cooking dailies, so you can increase the odds of getting the recipe by doing both every day and just hoping it eventually shows up.
Once you've learned it, you'll need the following:
- 8 Simple Flour: Purchased from any Cooking vendor.
- 4 Ice Cold Milk: Purchased from most innkeepers and lots of food vendors across classic Azeroth.
- 4 Mild Spices: Purchased from any Cooking vendor.
- 8 Small Egg: For Alliance, the most convenient place to farm these is off the moonkin in the caves east of Auberdine (Darkshore). For Horde, the most convenient place is off the dragonhawks in Eversong (outside Silvermoon).
- 1 Flask of Port: Purchased from most bartenders or alcohol vendors -- hit the closest tavern.
- 3 Mageroyal: Herbalists can get these on their own, but otherwise, just hit the auction house.