Translation:Ik was af, want jij hebt gekookt.
Because you're pointing someone out (emphasis), which requires jij.
But I wonder what about that situation or or about the other words in the sentence makes it a pointing out situation. Of course I know that jij has emphasis but I thought that emphasis was more a matter of personal choice. I can thank somebody for cooking without singling them out.
It doesn't sound right. I think it's because "Ik was af" is present tense. The present perfect is used to describe the past from the point of view of the present.
Thank you. I have frequently seen this description, "from the point of view of the present," but I don't know what it means. Every statement I make is from the point of view of when I make it: the present. Having tried to explain verb tense use in English to English learners, I recognize how difficult it can be to describe something that was absorbed without explanation in early childhood. So I won't hold you to further explanation.