- 16ouncesbittersweet chocolate(chopped)
- 1cupunsalted butter(cut into small cubes)
- ¼cupbrewed coffee(at room temperature)
- 1teaspoonvanilla extract
- Powdered sugar
- Adjust oven rack to lower-middle position and preheat oven to 325 degrees F. Grease 8-inch springform pan, line the bottom and sides with parchment, then grease the parchment. Wrap the outside of the pan with a double layer of aluminum foil and place in a 9x13-inch pan. Put a small pot of water on to boil.
- Using a stand mixer with a whisk attachment, beat the eggs on medium speed until doubled in volume, about 5 minutes.
Meanwhile, place the chocolate, butter and coffee in a large, heat-proof bowl set over a saucepan of barely simmering water. Stir occasionally until completely melted and smooth and very warm (the mixture should register 115 degrees F on an instant-read thermometer). Remove from the heat and stir in the salt and vanilla extract.
- Using a large rubber spatula, fold one-third of the eggs into the chocolate mixture until just a few streaks of egg are visible. Add the remaining eggs in two more additions, folding until the mixture is totally combined.
- Transfer the batter to the prepared springform pan and smooth the top. Pour enough boiling water into the 9x13-inch pan to come about halfway up the sides of the springform pan. Bake until the cake has risen slightly, the edges are just beginning to set and a thin glaze (like a brownie crust) has formed on the surface, about 22 to 25 minutes. The cake should register 140 degrees on a digital thermometer.
- Remove the cake from the water bath and set on a wire rack to cool completely to room temperature. Once cool, cover with plastic wrap and refrigerate at least 6 hours, or overnight (the cake can be refrigerated for up to 4 days).
About 30 minutes before serving, run a thin knife between the cake and sides of the pan; remove the sides of the pan. Place the cake on a serving platter, dust with powdered sugar and serve with a dollop of fresh whipped cream, if desired.