סימן קא סעיף א
כָּל הַמְּלָאכוֹת הַמֻּתָּרוֹת לַעֲשׂוֹתָן בְּיוֹם טוֹב, זֶה דַּוְקָא לְצֹרֶךְ אוֹתוֹ הַיּוֹם. אֲבָל לְהָכִין מִיּוֹם רִאשׁוֹן לְיוֹם שֵׁנִי (אֲפִלּוּ בְּרֹאשׁ הַשָּׁנָה), וּמִכָּל שֶׁכֵן לְיוֹם חֹל, אָסוּר. אַךְ אִם הוּא צָרִיךְ לְבַשֵּׁל בִּשְׁבִיל הַיּוֹם, מֻתָּר לוֹ לָקַחַת קְדֵרָה יוֹתֵר גְּדוֹלָה וּלְמַלֵּא אוֹתָהּ בָּשָׂר וְכַיּוֹצֵא בּוֹ, אַף עַל פִּי שֶׁאֵינוֹ צָרִיךְ הַיּוֹם כָּל כָּךְ, וְיוֹתִיר גַּם לַלַיְלָה אוֹ לְמָחָר. וְדַוְקָא בְּתַבְשִׁיל בַּקְּדֵרָה מֻתָּר, מִפְּנֵי שֶׁהַתַּבְשִׁיל מֻטְעָם יוֹתֵר כְּשֶׁמִּתְבַּשֵּׁל הַרְבֵּה בָשָׂר בְּיַחַד, וּבִלְבַד שֶׁלֹּא יֹאמַר בַּפֶּה, שֶׁהַמּוֹתָר יִהְיֶה לְצֹרֶךְ הַלַּיְלָה אוֹ לְצֹרֶךְ מָחָר, אֶלָּא יְבַשֵּׁל סְתָם. אֲבָל בִּשְׁאָר מַאֲכָלִים, אָסוּר לְהוֹסִיף בְּדָבָר שֶׁיֵּשׁ קְצָת טִרְחָא בְּמַה שֶּׁהוּא מוֹסִיף.
All Melachah1This includes even such chores that are not halachically considered melachos. See paragraph 2. (Magein Avraham, Mishnah Berurah 503:1) that is permitted on Yom Tov is permitted only if it is necessary for that day. But to prepare on the first day of Yom Tov for the second day,2Maseches Beitzah 2b. (even of Rosh Hashanah), and certainly for a weekday, is forbidden. However, if you need to cook for that day, you are permitted to take a larger pot and fill it with meat or something similar, even though you do not need so much for that day, and leave some for the evening, or for the next day.3Shulchan Aruch 503:1. Only in the case of cooked food, is this permitted. because it tastes better when a large quantity of meat is cooked in one pot.4The halachah is, that if you put it on the fire at one time, you are permitted to do so with all foods, since you are not performing additional labor, once it is on the fire. Regarding meat dishes, however, you are permitted to add to the pot even after it is on the fire. (Magein Avraham 503:2) This is permitted provided you do not expressly state that the leftovers will be for the night, or for the following day. It should be cooked without mentioning anything at all.5If you have already eaten that day, you may not cook a pot for the following day, even if you eat a piece of it today. (Shulchan Aruch 503:1) If you intentionally did it anyway, you may use it if you eat a piece of it today. (Magein Avraham, Beis Meir, Shulchan Aruch Harav) Eliyahu Rabbah rules that it is permitted, even if you intended to eat a piece of it, but ended up not doing so. Peri Chadash and Vilna Gaon rule, even if you eat a piece of it, it is forbidden, for it was done with dishonest intent. In the case of other foods, it is forbidden to add (to that day's needs), if even a little additional labor is entailed. because of adding to it.
תנא דבי אליהו כל השונה הלכות בכל יום מובטח לו שהוא בן העולם הבא שנאמר הליכות עולם לו אל תקרי הליכות אלא הלכות (נדה ע"ג.)