8 large eggs, cold
1 pound bittersweet or semisweet chocolate, coarsely chopped
½ pound unsalted butter, cut into ½ inch chunks
¼ cup strong coffee (optional)
confectioner’s sugar or unsweetened cocoa powder for decoration
1. Adjust oven rack to lower middle position and heat oven to 325°. Line bottom of 8-inch spring-form pan with parchment and grease pan sides. Cover pan underneath and along sides with heavy-duty foil and set in large roasting pan. Bring kettle of water to boil.
2. Beat eggs in electric mixer fitted with wire whip attachment at medium speed (speed 6 on a KitchenAid) until volume doubles to approx. 1 quart, about 5 min. (Or use hand-held mixer at high speed, also 5 min.)
3. Melt chocolate and butter (adding coffee, if using) in large heat-proof bowl set over pan of almost simmering water, until smooth and very warm (about 115° on an instant-read thermometer), stirring once or twice. (Or melt chocolate and butter together in a microwave at 50% power until smooth and warm, 4-6 min, stirring once or twice.) With large rubber spatula, fold 1/3 of egg foam into chocolate mixture until only a few streaks of egg are visible; fold in half of remaining foam, then the rest until mixture is homogeneous.
4. Scrape batter into prepared spring-form pan and smooth surface with rubber spatula. Set the roasting pan on oven rack, put in the cake pan and pour enough boiling water to come about halfway up side of spring-form pan. Bake until cake has risen slightly, edges are just beginning to set, a thin glazed crust (like a brownie) has formed on surface, and an instant-read thermometer inserted halfway through center of cake registers 140°, about 22-25 min. The cake may not look done, but trust the thermometer; it will continue to firm up as it cools. (If you use a 9-inch spring-form pan instead of the preferred 8-inch, reduce baking time to 18-20 min.) Remove cake pan from water bath and set on wire rack; cool to room temperature. Cover and refrigerate overnight to mellow (can be covered and refrigerated for up to 4 days).
5. About 30 min. before serving, remove spring-form pan sides, invert cake on sheet of waxed paper, peel of parchment pan liner, and turn cake right side up on serving platter. Sieve light sprinkling of confectioner’s sugar or unsweetened cocoa powder over cake to decorate, if desired. Serve with Triple Cherry Compote and (very) lightly sweetened freshly whipped cream.