@DiaNoNa.
Sorry, I unfortunately got it as I went through the game before I started my completionist mindset. For what little help it may provide, the in game description is:

"A recipe left by a legendary Black Whistle. The main ingredient only exists in the fifth layer. Eating it removes all fatigue."

I'm guessing it may have come from a side quest if it wasn't part of the normal progression. I'd say make sure there aren't any offered missions from Laffi, Habo, Ozen or the Caravan Fleet. If not that, then it may have been in the crafting missions from the guild or one of the missions you stumble across in Layer 4/5. Sorry I couldn't find anything decisive. Best of luck.

Hello. Well done. Just a small question, do you know where to get the recipe for Salted Rare Fish Roast? I can't find it for the life of me

@Yαɱαtσ.
For the Patchwork Hat, though I can't verify in my save having already completed it, it appears to be the reward for Shiggy's Quests.

Mild spoiler: Over the course of the game you can talk to Shiggy and Nat in their room at the Orphanage. Shiggy begins to give quests for specific monster kills or showing him particular relics he requests. Not all of the questline can be completed until notably late in the game due to some requests requiring a trip to the lowest layer. If you didn't start the quest line until later, I believe you can still start and progress it. I know you can refresh Shiggy's conversation availability by entering and leaving the abyss, but it may require less than that. If the next quest isn't up, just stop back and talk to him as you progress. It's been a while, but some of the quests in the chain may not be revealed till you reach a rank where it can be done.

Hopefully that helps.

Heya, I saw a thing asking for me to post this here by someone you blocked?

"Hi, DRayX and Paint✨ have asked in the past how to get Patchwork Hat."

I don't mean to pester or bother you, it just sounds like a reasonable request. Have a good one. :)

@Twilight Vulpine, Thanks for letting me know. Updated.

Thanks for the guide!

I was able to find and fight the Inter. Device [Layer 5] before doing the Layer 5 story missions at Ido Front and getting the White Whistle.