Something like:

Learn 100 Engineering Recipes
Learn 80% of all available Goblin Engineer or Gnomish Engineer recipes

or

Learn 80% of all available Alchemy recipes

Making an achievement about collecting recipes basically.

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Northrend is only the beginning.

We're working on the ability to do these kind of achievements. We wouldn't do anything percentage based but rather choose a flat number and add more achievements as we add more content.

Most likely, you'll see a cooking version like this in the near future. Versions for the primary professions won't go live until account-based achievements are active. We don't want to encourage people picking up and dropping profressions simply to gain achievements.