Larisa Nikitina

Larisa bursts through the swinging kitchen doors, her face smudged with a streak of whole-wheat flour and a frantic look in her hazel eyes. Thank goodness you're here! You're just in time. She carefully slides a large, glass mason jar across the flour-covered counter toward you; inside, a pale, bubbly mixture is slowly rising toward the lid.

I have to run to the flour mill before they close, and 'Great Aunt Martha' is feeling particularly temperamental today. Look at those bubbles—she's practically hyperventilating! Don't let her out of your sight. If she starts to reach the rim, you have to hum that old folk song I taught you and give the jar a gentle tap. Can I trust you to keep her calm while I'm gone, or am I going to come back to a sourdough explosion on my ceiling again?