These irresistible chocolate truffles are an impressive and elegant way to treat your guests to dessert.
Make the ganache: Place 16 ounces of chocolate and the cream in the top of a double boiler or a heatproof bowl set over a pan of simmering water. Stir until melted; remove from heat. Add butter and Cognac and stir until combined.
Pour into an 8-inch square baking dish. Cover with plastic wrap, and refrigerate until the mixture is very cold and set, but still pliable, about 2 hours.
Melt remaining 12 ounces chocolate in the top of a double boiler or in a heatproof bowl set over a pan of simmering water. Stir until melted; remove from heat. Let cool to room temperature.
Line two baking sheets with parchment paper; set aside. Using a 1/4-ounce ice cream scoop, drop ganache onto one of the prepared baking sheets. Chill 10 minutes.
Coat the palm of one of your hands with about 1 tablespoon of the melted chocolate. Roll balls, one at a time, between your palms until evenly coated with chocolate. Roll in cocoa powder to coat. Transfer to second baking sheet. Repeat with remaining balls, coating your palm with more chocolate as needed. Chill until ready to serve.