The moment of separating challah is an especially propitious moment for praying for family and loved ones. You may, of course, offer a personal prayer in your own words, or you can say one of the following.
May it be Your will, our G-d, the G-d of our Fathers, that You bless our dough, as You blessed the dough of our Mothers, Sarah, Rivkah, Rachel and Leah. And may we be blessed as in the verse: “You shall give the first yield of your dough to the kohen to make a blessing rest upon your home.” (Ezekiel 44:30)
Some have the custom to recite the following verse twice before reciting the blessing for separating challah (Sefer Chukei HaNashim):
May it be Your will, our G-d, the G-d of our Fathers, that the mitzvah of separating challah be considered as if I observed every one of its details. May my raising of the challah be considered as the sacrifice that was offered on the altar, which was willingly accepted. Just as giving the challah to the kohen in the past served to atone for sins, so may it atone for my sins and I shall be like a person reborn, free of sin and transgression. May I be able to observe the holy Shabbat and Festivals with my husband (and our children), and be nourished from the holiness of these days. May the influence of the mitzvah of challah enable our children to be always nourished by the hands of the Holy One blessed be He, with His abundant mercy, loving-kindness, and great love; and the mitzvah of challah be accepted as though I have given a tithe. And now, as I am fulfilling the mitzvah of challah with all my heart, so may the compassion of the Holy One Blessed be He be aroused to keep me from sorrow and pain always, Amen.