The Gift of Cheese

At /way 52.47, 26.80. there is a box, it's inside the Obsidian Rest to the right just in front of the cooking supplies vendor.
In the box there is an interactable cheese. When clicked on you'll recieve the [item=204871]
You can use the Recipe Rat every 5 minutes and it will give you some [item=204872]
The rat will only stay in your bags as long as you have Fine Aged Cheddar so make sure that you have some before heading to the rat, get 20 to be safe!

Once you've collected 30 [item=204872], combine them to get [item=204849]
Now cook up 50x[item=204848] and go find some [npc=4075] and feed them. When you've fed 50 you'll recieve the achievement and [item=204894]

Macro I used
/tar Rat
/use Charitable Cheddar
/stopmacro [noexists]

Falconhurst in Drustvar /way 25.71 is a good spot to find rats, but beware of the guards if you're horde.

Around 26 66 in Drustvar has a VERY HIGH concentration of "Rat". Happy Hunting!

1. ---

   When you're still on it, finish your old Zskera Vault [item=202252] negotiations for [item=204340]s or delete the Rat item. This seems to be the only old Recipe Rat interaction that may block progressing on the new one. I tried with characters who didn't acquire the [item=204073] or never met the Zskera Vault Recipe Rat and nothing was hidden.

   ---

2. 
   
3. If you haven't yet, learn [skill=2824] (later, skill 50 will be mandatory to learn the recipe for the soulbound [item=204848])
   
   
4. 
   
5. Purchase 20x Fine Aged Cheddar (or more, you'll need more for cooking later)
6. 
   
7. Head to Zaralek Cavern's Obsidian Rest on the [zone=13642] and interact with [object=398698] in a supply crate at /way #2133 52.43 26.82 Squeaking Swiss
   (make sure Step 1 & 2 are done, otherwise the cheese won't be visible)
8. 
   
9. To help people who went there unprepared, on your very first interaction with [object=398698] you will receive 1x Fine Aged Cheddar (flags hidden quest [quest=75648] complete) on top of the [item=204871] that hops into your bags.
10. 
    
11. As long as you have the [item=204871] in your bags, it will consume 1x Fine Aged Cheddar every ~3min and scurry away when there's no cheddar left.
    (unless you've acquired all recipe scraps, Squeaking Swiss will be visible again when you lost the Rat)
12. 
    
13. Every 5min you can now [spell=407366] before the Recipe Rat (by using the [item=204871]) to get a random number of [item=204872].
14. 
    
15. When you did acquire 30x [item=204872] this way, the rat will eventually escape forever, but you can now [spell=407373] to get the [item=204849].
16. 
    
    
    
17. Learn the recipe, and get all the ingredients needed (which is quite a "ride") to cook 50x [item=204848].
    (depending on your cooking skills this will take up to: 50x Fine Aged Cheddar , 20x Spicy Sharp Cheddar , 10x [item=162555] , 10x Gold Bar)
    
    
18. 
    
19. Travel the world to find Rats (literally critters with "Rat" as their names), target them, and use the [item=204848] to complete your The Gift of Cheese achievement and eventually be rewarded with [item=204894].
    
    
20. 
    
21. Patch 10.1.5 addition: When you summon [npc=204036] on a character with [skill=2824] skill 50 (and at least one of the recipes unlearned), our befriended Recipe Rat will now train them the recipes for Deviously Deviled Eggs and Charitable Cheddar without needing to locate him again in Zskera Vaults or Zaralek Cavern.
22. 
    

Kudos to Kamboozle for sharing the Squeaking Swiss find on the Secret Finding Discord.