I've looked thought the whole Witton and i can't find. I checked the shop and there wasn't a dialog or a option to buy it and i don't know where to look now. Can you tell me where exactly is it?

You have to check the stuff on the tables in shops. They're not the same as what the store clerk sells.

The recipe is on the white table in the top left corner of the magic goods shop in Witton.

Okay found it thanks for the help.