Adapted from Cook's Illustrated
12 ounces semi-sweet chocolate, chopped
1/2 cup heavy cream
2 tablespoons light corn syrup
1/2 teaspoon vanilla (or 2 tablespoons of your favorite liqueur)
1 1/2 tablespoons butter, at room temperature and cut into small pieces
1 cup cocoa powder
1/4 cup powdered sugar
Line 8 inch square pan with foil. Set aside.
In a medium bowl, microwave chocolate, stopping and stirring at 30 second increments, till the chocolate is almost completely melted. Heat cream in microwave safe measuring cup till warm, about 30 seconds. Stir corn syrup and vanilla into cream, then add to chocolate. Cover with plastic wrap and let sit for a few minutes. Stir till mixture is uniform, then add butter and mix till well incorporated.
Spread chocolate ganache evenly in prepared pan and allow to cool at room temperature for 2 hours. Cover and transfer to refrigerator. Cool at least 2 hours.
Sift together cocoa and powdered sugar, then sift again. Place in flat pan, suitable for rolling the truffles.
Remove chilled ganache from pan by lifting up foil. Peel off foil and set ganache on cutting board. Let warm up a couple minutes, then cut ganache into 64 equal sized squares, starting by cutting the large square into 4 even parts, then those 4 squares into 4 even parts, then repeating twice more till you have 64 squares.
Dust hands with cocoa mix and roll each square into a ball. Roll balls in cocoa, shake off excess and place truffles in an air tight container. Store in refrigerator, and let come to room temperature before serving.