If you've never been in the presence of a day-old calf, they happen to be disconcertingly large. Recently I followed one—the color and size of a golden retriever—as it stumbled around Diane St. Clair's barn, bleating loudly. Rain pounded on the roof, my boots were spattered with mud, and my neck ached after a five-hour drive. But it hardly mattered. I'd come to this sparsely populated corner of western Vermont to taste the country's most sought-after butter.