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The Missionary's Cookbook 1 is one of the many Key Items found throughout Elden Ring, sold by Merchant Kale in West Limgrave.
The Missionary'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:
Purchased From: Merchant Kale at the Church of Elleh in West Limgrave. It is sold for 150 Runes.