Question: What is the Kaffara for breaking one's fast intentionally?
Answer: One who has broken his fast intentionally he must, in addition to making up the qadha of that day, fast for two months the first thirty one days in a row. Or he must feed 60 poor Momins to their fill or he must give 750 grams of wheat to each one of them. If none of these is possible for him, he is free to either fast for eighteen days or feed as many poor people as he can. If he cannot do this also, he must ask Allah for forgiveness even if he has to say "Astaghferullah" once. And it is an obligatory precaution that if he is able later, he must give the kaffarah. Of course, the kaffarah is obligatory in the case that his ignorance was not due to his own negligence in learning the rulings. However, if he has grown up in a place that without his own choice, he was unaware of the rulings, then it is obligatory that he must make up that day only.

https://www.sistani.org/english/qa/01236/