so, as far as I understand you want to ask someone to make some cookies for you? it wasn't easy to guess, though, so maybe I am wrong. :-) испечешь мне печенья? you may say this to a person of your age or younger, to a member of your family or to a friend. but if it is your friend's mother or your boss :-) you should say испечёте мне печенья? I hope it will help. :-)

maybe he means internet browser's cookies?))