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The Armorer's Cookbook 1 is one of the many Key Items found throughout Elden Ring, located at a Kaiden Mercenary Camp in West Limgrave.
The Armorer's Cookbook 1 is a Key Item Recipe Book that will unlock extra crafting recipes once you have obtained it.
This includes the following recipes:
You can find the Armorer's Cookbook 1 at the Northern Mercenary Camp in West Limgrave, just to the east of the Agheel Lake North Site of Grace, where many of the mercenaries have set up a guarded outpost.