To make panettone — traditional panettone, coaxed from a stiff, naturally leavened starter — is to embark on a long, expensive and unpredictable journey, risking disaster at every turn. Roy Shvartzapel, a baker in San Francisco, refers to the Italian bread as “the Mount Everest of baking.”

“You’d be hard pressed to find a more challenging dough,” said Mr. Shvartzapel, 40, who owns the mail-order panettone business From Roy. Panettone dough is wildly sensitive, demanding and occasionally infuriating, following its own unique logic and schedule. Built up in stages, it can’t be rushed or made to wait. It requires an investment of ingredients, a deep understanding of fermentation and attention to pH levels, along with constant attention.