I think John would actually be a good baker. Where are Simon isn't (or just doesn't care to bake). John can go off script with baking, too, because he understands what's happening with the ingredients.

Whereas I don't think Simon cooks from that perspective even if he does understand the chemistry

And I think John is at least a decent cook, too. Of the two, Simon is the better cook. It just comes so naturally to him.

A lot of John's cooking knowledge is from being really good at chemistry.

An additional thought; Simon learned a lot from watching the Food Network. He's spent a lot of nights awake on his couch, idly flipping through the channels even though he inevitably always settles on the same one. That progresses to him picking up some cookbooks as well.

Johnny has no idea that Simon can cook and certainly doesn't know he's a good cook. When they get together and begin to spend leaves together, Johnny finds out one night when Simon rouses him from his sleep with a hot plate of the best pasta Johnny thinks he's ever tasted.

It's a far more productive time than lying paralyzed by fear in bed while he clutches the sheets like a scared child afraid to even close his eyes. It lets him pretend he's more put together than he is.

Sometimes, when he wakes from a nightmare and can't go back to sleep, he'll get up and cook. The smells bring him back, and the pan's sizzling keeps him grounded.