yom tov has a melacha allowance that shabbos does not: “no work at all shall be done on them, only what every person is to eat, that alone may be prepared for you” (shmos 12:16). cooking for the day’s food is permitted on yom tov. shabbos has no such allowance. so when the two land on the same day, which one wins?

1. on yom tov that falls on shabbos, can a person cook for the meals of the day, since eating is a need of the day? or does shabbos push off the ochel nefesh allowance entirely, so everything must be cooked before?

2. if cooking is allowed, is it the full yom tov allowance or a cut down version? can one light a fire from an existing flame, adjust a flame, bake? or only reheat?

3. what takes precedence when the rules collide: yom tov permits carrying and cooking for food needs, shabbos forbids them. does the torah read that day as shabbos with a yom tov exception, or as yom tov with extra shabbos rules? and is eruv tavshilin part of this, or does that only deal with friday cooking for shabbos?

4. practically: most people just heat up food cooked beforehand. what is actually permitted lechatchila, and what do people do that the halacha never allowed?

bottom line: when yom tov falls on shabbos, what exactly is permitted in the kitchen, what takes precedence between the two days’ rules, and why?