Shulchan Arukh, Orach Chayim 482/שולחן ערוך·אורח חיים תפ״ב

1The law of one who does not have protected matzah. Containing 1 paragraph: One who only has a olive-size portion of matza recites the blessing of, "about eating bitter herbs," and eats [them]. And when he finishes his meal with matza that was not protected, he recites the blessing, "about eating matza," eats that kazayit and does not eat anything after it. Rema: And one who only has three matzot for the [first] two nights should recite on the first night, "about eating matza" and "who brings forth (ha-motzi) - and likewise with the sandwich (of matza and bitter herbs) - all upon the [first] piece; and the two matzot are [held] for the second night. (Abudarham in the name of Ibn Yarchi)