I puzzled some more over my invisible ingredients and realized I forgot a very important one (now added to the list). Who are you baking with? I find the company I keep in the kitchen is half the fun. Be it a housemate or two passing through, or an assistant baker with lots of catching up to do, some good conversation (while dangerously distracting) has wonderful side-effects on your baking. Many of my best baking memories have great conversations attached.
So while you're out shopping for butter, eggs and chocolate chips, be sure to send in the order for a friend's company too.