Instructions

1. Preheat the oven to 350°F. Butter a 9-inch round cake pan, line the bottom and sides of the pan with parchment paper, and butter parchment. Set the pan aside.
2. In a large heatproof bowl, whisk together the eggs, egg yolks, and sugar. Set the bowl over a pot of very gently simmering water (the bottom of the bowl should not touch the water), and stir just until the mixture is room temperature. Remove the bowl from the heat and beat the mixture with an electric mixer on medium speed until quadrupled in volume, 15–20 minutes. In a second medium heatproof bowl set over the pot of simmering water, combine the chocolate and coffee, stirring often, until melted. Remove from the heat and set aside. In a third, chilled, medium bowl, use a balloon whisk or the electric mixer to whip the cream until soft peaks form.
3. Fold one-quarter of the egg mixture into the melted chocolate, then fold the chocolate-egg mixture and whipped cream into the remaining egg mixture. Pour the batter into the prepared pan and set the pan in a larger roasting pan. Pour hot water into the roasting pan to a depth of 1 inch, then transfer to oven and bake cake until a toothpick inserted in center comes out clean, about 1 hour. Turn off the oven, leave the door ajar, and let cake rest without removing for 30 minutes. Remove the cake from the oven in its water bath and let rest at room temperature for 30 minutes more. Remove the cake from the water bath, invert onto a plate, and peel off and discard the parchment paper. Serve warm or at room temperature with whipped cream and shaved chocolate (if desired).