SAN FRANCISCO — It takes three days to make a cruffin, a muffin-croissant hybrid that is the signature of Ry Stephen, a 28-year-old pastry chef. His shop, Mr Holmes Bakehouse, has been open three months and inspired a wild following, with customers lining up early to buy the ice-cream-cone-shaped cruffins, which reliably sell out before the line is gone.

“It creates its own frenzy,” said Rebecca Flint Marx, editor of San Francisco Magazine’s food section, who noted that not only are cruffins a cult item — and at $4.50, relatively affordable — but they are also camera-ready, as photos on Instagram attest. Fillings include caramel, strawberry milkshake or Fluffernutter cream (among other flavors), depending on Mr. Stephen’s mood.

Now, the tempting sweet may have inspired a crime. Overnight last week, a thief stole the recipe for cruffins, and Mr. Stephen’s 230 other recipes, from binders in the bakery’s kitchen. Nothing else in the store was touched: not money, valuable baking equipment, an iPad or other computers. And while Mr. Stephen has copies of the recipes on his office computer, and the store opened almost on time the next morning, he was understandably upset.

“It sickens me a bit,” he said.

In a food-crazy city where every consumer is a Yelp critic, the theft of the recipes — which the police are investigating — inflamed the demand for cruffins, the West Coast’s answer to New York’s cronut. (Both have croissant bases but are shaped differently, and a cronut is fried while a cruffin is baked). By Monday morning, the news of the missing cruffin recipe struck some people as just another reason to visit Mr. Stephen’s bakery.