would anyone happen to know which jar file that minecraft keeps their core recipes in?
They're in the main Minecraft client JAR file (or server JAR if you're running a server).
You'll find the client in (for example) .minecraft\versions\1.12.2\1.12.2.jar, and they'll be under the \assets\minecraft\recipes folder within the JAR.
Thank you. I"ve been busy the last few days. I'm taking an RPG style spin on minecraft so I want to change a few items to make more sense and reflect technological progression (as well as requiring certain "quests" to be completed or "rep" gained before some things are "taught" to the player).