The best butter I've ever tasted was a tiny, bright yellow disk that was delivered to my table with bread at Restaurant Jean in Paris. Each bite contained a universe of flavors—saline, floral, earthy, nutty—painted on a canvas of cream. When I asked the chef, Benoit Bordier, where I could buy some, he told me it might be hard to find. "This butter is delivered to us once or twice a week directly from Brittany," he said, explaining that it was made by a man who shared his last name but was not a relative. The following night, at a restaurant called Spring, run by an expatriate American chef named Daniel Rose, I tried an equally exquisite butter, this one flecked with seaweed. When I asked Rose about it, he said, "It's Bordier butter. I pay more for it than I do for my foie gras." More intrigued than ever, I paid a visit the next day to the Quatrehomme cheese shop in the city's Saint-Germain neighborhood. The owner, Marie Quatrehomme, told me that Jean-Yves Bordier makes a traditional style of hand-churned butter, known as beurre de baratte, near St-Malo, a city in northern Brittany. She explained that Bordier customizes his product to the tastes of the individual chefs he sells to and fashions it by hand into different shapes—a cone, say, or a diamond. She showed me four different varieties: beurre doux (plain cultured butter), beurre au sel (salted butter), beurre au sel fume (smoked-salt butter), and beurre aux algues (seaweed butter).