Jonah Magnus never learned to cook.
Therefore Elias Bouchard, head of the Magnus Institute, London, cannot cook. He never bothered. Having grown up a Victorian Gentleman ™ he considers it to be beneath him.
He has however reached the point where he knows that it’s embarrassing that he doesn’t know how to turn on a stove. (Peter has made fun of him relentlessly). He still refuses to learn, but refuses to be mocked.
And so, the performance begins.
“I’ve seen Elias cook.”
“Did you? Or have you just seen him plate things?”
“But…we’ve cooked together!”
“Really? Or was he standing by the sink, washing one vegetable for over an hour while you did all the work?”
Personally, I think Peter’s the one who’d be confused by a stove. Elias is a very self-sufficient, adaptable man who is happy doing menial work like paperwork. I don’t think cooking is going to be beneath him. I don’t think he’s that vain (actually, I think he’s the opposite of vain; this is a man who was happy being seen as the bumbling, but well-meaning boss for years and a ‘waste of a suit’). Peter, meanwhile, is a lazy little rich boy who sits in his captains cabin all day and has his food delivered to him by his first mate. I can’t really see him cooking when he canonically has food delivered to him 99% of the time, much less being any good at it.
I don’t think Peter would try to hide his inability to cook though. He doesn’t need to know how to work a stove; that’s for peasants people who don’t have enough money to hire personal cooks.