Should I mix my puppys old food with her new homecooked food??

Hello I have a 9 week old chi. And at the moment im giving her what the breeder was giving her, which is cesar dog food(soft food) I know that to change a puppys food u usually have to mix the new with the old little by little but what if its homecooked...do I still have to mix it or can I jus give it to her right away w/out mixing???