Julia's Kitchen by Brenda A. Ferber

Cara Segal is at a sleepover the night a fire breaks out at her house, killing her mother and sister. Her father survives, but is so distraught over their loss that he is unable to answer Cara's questions, and he buries himself in his work. After 41 days of being the only one who can make Cara smile, her best friend, Marlee, tells her she wants the old Cara back. One day, Cara's father gives her a box of items that had survived the fire. Among other things, her mother's recipe box was intact. Cara begins to heal when she decides to keep her mother's homemade cookie business, Julia's Kitchen, alive.