Chapter 12. The Seventh Day of Pesach That Falls on Friday

[See the sources of these laws at length in Iyunim Pesach, section 1]

Kitniyot on Shabbat Isru Chag of Pesach
1. If the Seventh Day of Pesach falls on Friday, Ashkenazim who follow the custom not to eat kitniyot on Pesach may eat kitniyot on Shabbat. This is because they were not prohibited during bein hashmashot on account of Shabbat itself, but only due to the doubt that it might still be the Seventh Day of Pesach; this does not render them muktzeh for the entire Shabbat [1] .

Cooking Kitniyot on the Seventh Day of Pesach for the Following Shabbat
2. One should refrain from cooking kitniyot on the Seventh Day of Pesach for the needs of Shabbat, since some authorities maintain that anything forbidden to eat is also forbidden to cook, out of concern that one may come to eat it [2] .

[1] Shulchan Aruch (section 665, paragraph 1), Biur Halacha (ad loc.), and Chazon Ish (section 49).
[2] See the explanations at length.