2. Place the bittersweet chocolate in a small heatproof bowl. Pour the boiling water over the chocolate and whisk until smooth. Let cool to room temperature before using.

3. Whisk together the cocoa powder with the flour, confectioners' sugar, salt and cacao nibs in a large bowl until thoroughly combined.

4. In the bowl of a stand mixer fitted with a paddle attachment, beat the butter with the brown sugar and granulated sugar on medium speed for 2 to 3 minutes, until light and fluffy. Beat in the eggs, one at a time, and then beat in the vanilla. Add the cooled melted chocolate mixture and beat until just combined. With the mixer on low, add the flour mixture and beat until just combined.

5. Pour the batter into the prepared pan, smooth the top, and bake for about 45 minutes, until the edges begin to pull away from the sides of the pan. (Don't use a cake tester for this cake -- it won't come out clean.) Let the cake cool in the pan on a wire rack for 1 hour and 30 minutes. Do not try to take the cake out of the pan any earlier than this! Then invert the cake onto the rack and let it cool completely (another 1 hour and 30 minutes to 2 hours). Drizzle the cake with the ganache (see recipe below) and let it set for 5 to 10 minutes before serving. The cake will keep in an airtight container at room temperature for up to 3 days.

Bittersweet Chocolate Ganache

4 ounces (115 g) bittersweet chocolate, chopped

1/3 cup (80 ml) heavy cream

Pinch of fleur de sel

1. Put the chopped bittersweet chocolate in a heatproof bowl. In a small nonreactive saucepan over medium-low heat, heat the cream to scalding (when little bubbles form around the edge of the cream but before it begins to boil). Pour the cream over the chocolate, cover, and let sit for about 3 minutes, or until the chocolate has melted. Add the fleur de sel and whisk together until smooth and uniform.

(Diane Rossen Worthington is an authority on new American cooking. She is the author of 18 cookbooks, including "Seriously Simple Holidays," and also a James Beard award-winning radio show host. You can contact her at www.seriouslysimple.com.)