Oh, thanks for the help!

I didn't actually have to create the soup stock though. I just had to make a devilbelly meatball out of the foulbelly meatball and speak to Prudentia afterwards. Still, that part of the quest was kinda confusing. Especially having Prudentia stand there out of reach and the journal insisting that I have to speak to the NPCs in the culinarian's guild. I guess I could've figured it out if I had just tried a little harder though...