Wow..... have you thought about enrolling your child in a child's cooking class? There are sometimes "Mommy and me" food classes. That might be a way to get him to try some more foods, also.... and give you some more meal ideas.
I like the way you put it that if he was going to cook with you, he has to try it. Some kids do have food aversions, or texture issues.... my kids never had problems with that, so I don't know how to suggest a way around that.
We didn't make meal time a battle, I just said they didn't have to eat what I cooked, but if they didn't eat what I cooked, they could wait until the next meal. (They didn't get the option of a sandwich or bowl of cereal, either.) My kids grew up to be fantastic eaters, willing to try just about everything this way. (One daughter still hates peas, though... oops!) There were some things I didn't MAKE them eat, like sauerkraut (but they all love it), but cooked the things hubby and I liked.
Some people do not like things blended together, but I love casseroles! It is really hard to give meal ideas if we don't know what kind of things you and your family usually eat.