On Pesach someone cut an onion put it in a kugel and proceeded to bake it. They then realized that the knife they had used was a regular knife used the whole year (one of the children took it out and so it was used by mistake). It’s a “chametz” knife or at least a “sofek chametz” knife. What’s the din on the kugel, the pan it was cooked in, and the oven?
The kugel may not be eaten. The pan that came into contact with the kugel should not be used directly with food. The oven is fine.
A knife that was used for cutting onions transfers the chametz taste to the onions, and therefore the onion is considered “chametz.” Therefore, the kugel may not be eaten on Pesach, because of the chametz taste of the onions.
The pan that came into contact with the onions should not be used on Pesach, unless covered; the oven, provided it didn’t come into direct contact with the kugel, is fine.
See Mishnah Berurah 447:54; in circumstances of loss there is room for leniency based on the Chazon Ish, Orach Chaim 119:11, but in general one must be stringent, as ruled by the Mishnah Berurah and the majority of poskim.
For the pan, the beliah, according to some poskim, will not carry the full stringency of the onions themselves (see Chayei Adam 48:16, and several poskim who rule this way), and in addition to the fact that the knife is only “safek chametz,” there is some room for leniency — but it should nonetheless be used covered, and to kasher it for next Pesach.