Tweaking the kosher law in a nonstandard setting
"You must not cook a young goat in its mother's milk."This is the food equivalent of Powered by a Forsaken Child. Contrary to the description, it is not necessarily limited to mixing meat and milk. Especially, it is not limited to mixing the meat of goats and their mother's milk. The dietary law above was more about the risk of doing so, creating a cannibalizing effect. And That's Terrible. There are also some animals you can't eat, such as shellfish or pork. Great. Now imagine this applied to fiction. The creators have actually thought about the laws, and applied them to the setting. If it's a realistic setting, you might have actual kosher with a few discussions on what should also be forbidden. If it's a fantasy/science fiction setting, there might be analogous rules and regulations, such as not eating Eldritch Abominations because they're shellfish.