It's a real cookbook! The author did her best to mimic the in-game food as realistic recipes. The recipes are definitely a bit of both, one of my favorites from the first one were "chuchu jellies" that had different flavors for different colors of preserves, like spicy or minty. They also vary greatly in difficulty, some are quite simple while others require a good bit of effort, like the bottling for the jellies. The author got into cheesemaking since the main draw to it seems to be a Hateno cheese that was said to take a few months to make.