The Ultimate Flourless Chocolate Cake

1. Adjust oven rack to lower-middle position and heat oven to 325 degrees. Grease 8-inch springform pan, line with parchment paper, then grease sides. Wrap outside of pan with two 18-inch-square pieces of aluminum foil; set in roasting pan. Bring kettle of water to boil.
2. Using stand mixer fitted with whisk, whip eggs on medium speed until doubled in volume, about 5 minutes.
3. Meanwhile, melt chocolate with butter and coffee in large heatproof bowl set over saucepan filled with 1 inch of barely simmering water, stirring once or twice until smooth and very warm (should register about 115 degrees). Using large rubber spatula, fold one-third of egg foam into chocolate mixture until few streaks of egg are visible. Fold in remaining foam in 2 additions until mixture is totally homogeneous.
4. Scrape batter into prepared pan and smooth top with rubber spatula. Set roasting pan on oven rack and pour enough boiling water into roasting pan to come about halfway up sides of springform pan. Bake until cake has risen slightly, edges are just beginning to set, thin glazed crust (like a brownie crust) has formed on surface, and cake registers 140 degrees, 22 to 25 minutes. Remove cake pan from water bath and set on wire rack; let cool to room temperature. Cover and refrigerate overnight. (Cake can be refrigerated for up to 4 days).
5. About 30 minutes before serving, run thin knife between cake and sides of pan; remove sides of pan. Invert cake onto sheet of waxed paper, discard parchment, and turn cake right side up onto serving platter. Dust with confectioners’ sugar, if using, and serve.

Even though the cake may not look done, pull it from the oven when it registers 140 degrees. It will continue to firm up as it cools. If you use a 9-inch springform pan instead of the preferred 8-inch, reduce the baking time to 18 to 20 minutes.