This is just my own opinion about how to possibly assign credits. Everyone is different in how they do this, so this is just MY own personal way of thinking and nothing else. It is NOT a recommendation. We don't bind ourselves slavishly to traditional ways of thinking about school, so take this all with a grain of salt.
If you wish to use Guest Hollow's High School Chemistry in the Kitchen, here are some of the things I think are covered as subjects. I won't list the amount of credits, as credit systems vary. I will give my general ideas about them, though.
Chemistry - I personally believe that this curriculum is worth a full year of science credits, but the activities are an important component of those credits.
Home Ec / Cooking / Food Science - Cooking real meals & lots of delicious goodies is a large component of this year's activities. Your student will be learning a lot about food science and developing cooking skills & knowledge.
History - I've marked in the book list which books can be used for history credits. Other ways to add in additional history credits besides the reading:
Possible titles for history credits:
Hopefully this helps you think through how you'd like to assign credits for Guest Hollow's High School Chemistry in the Kitchen.