סימן קי סעיף ד

אֵין לָשִׁין עִסָּה גְּדוֹלָה יוֹתֵר מֵשִּׁעוּר חַלָּה. וְטוֹב לְמַעֵט, כִּי שִׁעֲרוּ רַבּוֹתֵינוּ זִכְרוֹנָם לִבְרָכָה, שֶׁאִם הָעִסָּה גְּדוֹלָה יוֹתֵר מִשִּׁעוּר חַלָּה, אִי אֶפְשָׁר לַעֲסֹק בָּהּ בְּפַעַם אַחַת, וְחֵלֶק מִמֶּנָּהּ מֻנָּח בְּלֹא עֵסֶק, וְיֵשׁ לָחוּשׁ פֶּן יִתְחַמֵּץ. אִם לָשׁ עִסָּה רַכָּה, לֹא יוֹסִיף קֶמַח לְעַבּוֹתָהּ (תנ"ו תנ"ז תנ"ט).

No dough should be kneaded that is larger than the quantity of dough that is subject to the separation of challah.¹A quantity of flour that equals forty-three and one-fifth eggs is subject to the law of challah. (see Chapter 35:2) It is better to make it smaller, for our Rabbis of blessed memory estimated, that if the dough is larger than the quantity of dough that is subject to challah, it cannot be worked at one and the same time;²There are some Poskim that are lenient and permit even larger quantities, since in our times there are large ovens and many people are involved in production which makes it unlikely that it will become chametz. Mishnah Berurah says, however, that it is best to be stringent, even in these times and to follow the opinions of the Shulchan Aruch. (Mishnah Berurah 456:7, Shaarei Tzion 10) thus part of it will be left unworked, and there is reason to fear that it may become chametz. If the dough you are kneading is loose, flour should not be added to thicken 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.)