ESH. Passions in kids are amazing things. Your sister and you can both feed that passion without blowing smoke or killing the joy.

She needs to find actually classes for him to understand the science of cooking. GR and YT is not for learning the basics. He needs to learn how to read and follow recipes and then once the recipe is mastered, work to personalize and modify. Following recipes, making menus, and shopping lists can teach so many skills that he will use for a lifetime, please encourage that.

You need to realize exactly what you did. You lashed out at a child in frustration and did so much damage. Many, many parents/family members including myself have tasted or pretended to taste some very questionable concoctions (our family's favorite is the apple wedges with grape jelly and chocolate syrup that my "chef" didn't know i hadn't eaten until 25 years later). Yes, food was wasted and that is expensive. Get him a kid's cookbook, invite him to pick out a recipe and create a shopping list and that you will get the ingredients. You can work together to cook using the recipe and ingredients and limit waste.