Cooking kitniyot in Pesach pots before Pesach or during Pesach, lechatachila, to eat the kitniyot on Shabbat Isru Chag. Allowed for Ashkenazi?
No Ashkanazim do not eat or cook with kitneyot on Pesach
An Ashkenazi cannot cook kitniyot for a Sephardi on Pesach? Kitniyot is only forbidden to eat for an Ashkenazi.
True.
So, if an Ashkenazi can cook kitniyot, is the residue in the pot batel?
Yes. On the assumption that the purpose of cooking was not to be mevatel the residue. Which would be a real strange thing, if that was the purpose.
אין מבטלים איסור לכתחילה
This is a concept that says that you get fined or punished because you deliberately tried to play a game and take an issur and be mevatel it
That only applies if the person being mevatel the issur deliberately intended to do it for this purpose specifically.
To clarify. We are ashkenazi. Can we cook with kitniyot in our pesach dishes before pesach and then use the dishes on pesach (without kitniyot)?
Yes