Cooking instead of boiling would be better
"boiling" is just accepted, not suggested. But frankly, it makes so little sense here that I guess I will just delete it altogether.
I tried “cookery”, but it was not accepted. Wouldn’t that be fine, too?
Seems to make sense, added.
His hobby is cooking. (OK in English but not accepted here)?
"Gotowanie to jego hobby" and "Jego hobby to gotowanie" are technically two different sentences with different grammatical subjects. Your English translation is for the second one.