The chef and restaurateur Thomas Keller is now in the chocolate business: a bean-to-bar partnership with Armando Manni, a Tuscan olive oil producer. The idea was born five years ago, when the men were discussing the antioxidant properties of dark chocolate and olive oil. The results, called K & M Extravirgin Chocolate (they say it “K plus M”), are made in a former warehouse in Napa, Calif., where the cacao undergoes a special, gentler process to preserve the bean’s antioxidant properties. Mr. Manni’s olive oil is used in place of cocoa butter. The 75 percent cacao bars come in three varieties, according to the source of the chocolate. The Peruvian bar has coffeelike depth, the bar from Ecuador is smooth with woodsy hints of chestnut, and the Madagascar bar is spicy with notes of pineapple and passion fruit. You do not taste the olive oil.