Daf Yomi - Yoma 46 - Bishul even if it Cooked after Shabbos

The Chemdas Yisroel brings a Yerushalmi that holds that the burning of the fats on the mizbeach would be considered bishul regarding Shabbos. According to this, he asks the following question. why is it permitted to burn the fats on the mizbeach in the beginning of Shabbos, it would be advantageous to wait until a few minutes prior to sunset, while they still would be fulfilling the mitzva of haktara (which must be done on Shabbos), they would not have to transgress the issur of bishul?

He proves from this question that if one initiates the process of bishul on Shabbos, even though it does not cook until after Shabbos, he would still be violating the issur of bishul.

Does anyone have any other proofs to this or kashos on this yesod?