Well done, @Left_Empty ! It is indeed Atelier Sophie: The Alchemist of the Mysterious Book! (and it's available on Steam, in case you didn't know)
It's funny that @sharaleo guessed Recettear, because both games have a lot in common in terms of theme and "feel" (even if the gameplay is considerably different). Anyway, it's a great game I'm having a great time with.