Siman 432
Presented here for study, not as a practical ruling. The Shulchan Aruch rules by Sephardi custom, the Rema's glosses by Ashkenazi custom, and the Kitzur follows Ashkenazi custom. For a practical question, ask your rabbi.
א קֹדֶם שֶׁיַּתְחִיל לִבְדֹּק יְבָרֵךְ: אֲשֶׁר קִדְּשָׁנוּ בְּמִצְוֹתָיו וְצִוָּנוּ עַל בִּעוּר חָמֵץ. וְאִם הִתְחִיל לִבְדֹּק בְּלֹא בְּרָכָה, יְבָרֵךְ כָּל זְמַן שֶׁלֹּא סִיֵּם בְּדִיקָתוֹ, (כָּל בּוֹ); וְיִזָּהֵר שֶׁלֹּא יְדַבֵּר בֵּין הַבְּרָכָה לִתְחִלַּת הַבְּדִיקָה. וְטוֹב שֶׁלֹּא יְדַבֵּר בִּדְבָרִים אֲחֵרִים עַד שֶׁיִּגְמֹר כָּל הַבְּדִיקָה, כְּדֵי שֶׁיָּשִׂים אֶל לִבּוֹ לִבְדֹּק בְּכָל הַמְּקוֹמוֹת שֶׁמַּכְנִיסִים בּוֹ חָמֵץ.
1 The Laws Pertaining to the Blessing Recited Over the Search For Chametz, 2 Seifim: Before one begins to search for chametz, the blessing "אשר קדשנו במצותיו וצונו על ביעור חמץ" is said (and if one begins to check without making the blessing, he then makes the blessing) during the entire time that he has not finished checking (Kol Bo). One must be cautious that one not speak between the blessing and the beginning of the search. And it is a good thing not to speaking of other things until one finishes all of the search, in order that he may put his heart into checking in all the place that chametz may enter.
ב בִּבְרָכָה אַחַת יָכוֹל לִבְדֹּק כַּמָּה בָּתִּים. וְאִם בַּעַל הַבַּיִת רוֹצֶה, יַעֲמִיד מִבְּנֵי בֵּיתוֹ אֶצְלוֹ בְּשָׁעָה שֶׁהוּא מְבָרֵךְ, וְיִתְפַּזְּרוּ לִבְדֹּק אִישׁ בִּמְקוֹמוֹ עַל סְמַךְ בְּרָכָה שֶׁבֵּרַךְ בַּעַל הַבַּיִת. הַגָּה: וְנוֹהֲגִים לְהַנִּיחַ פְּתִיתֵי חָמֵץ בַּמָּקוֹם שֶׁיִּמְצָאֵם הַבּוֹדֵק, כְּדֵי שֶׁלֹּא יְהֵא בִּרְכָּתוֹ לְבַטָּלָה, (מַהֲרִ"י ברי"ן). וּמִיהוּ אִם לֹא נָתַן לֹא עִכֵּב, דְּדַעַת כָּל אָדָם עִם הַבְּרָכָה לְבַעֵר אִם נִמְצָא. (כָּל בּוֹ).
2 With one blessing, one can check several houses. And if the head of the household wishes, one or more members of his household should arise at the time he makes the blessing, and they should then spread out to check, each person searching his designated place, relying upon the blessing said by the head of the household. Rema: It is our custom to leave small pieces of chametz in a place where the searcher will find them in order that his blessing not be in vain (Mahar"i; Ber"in). However, if one did not so [place bread] it does not hold back the need for the blessing because everyone has in mind to burn if he finds [bread]. (Kol Bo).