Position the oven rack to the lower third of the oven (lower center) and preheat to 325F. Line the bottom of the pan with parchment paper and grease the sides. Set the pan on a wide sheet of heavy duty foil and wrap the foil up the sides without tearing it. Set the pan in a larger baking pan or a roasting pan. Bring a kettle of water to a boil. Use a handheld mixer to beat the eggs at high speed for 5 minutes until the volume of the eggs doubles to approximately 1 quart. If you have to use a heavy duty mixer such as a Kitchen Aid, use the whisk attachment and speed 6, beating to the same volume which will take about the same amount of time.
Meanwhile melt the chocolate, butter and coffee in a large heat proof bowl. Either set in a pan of barely simmer water or in the microwave at 50% power for 4-6 minutes, stirring frequently until them mixture is smooth and warm (about 115 degrees). Fold 1/3 of the egg foam into the chocolate mixture with a large rubber spatula until just a few streak of egg are still visible; fold in half of the remaining foam likewise.
Fold the remaining foam into the batter until completely incorporated. Scrape the batter into the prepared spring form and smooth the surface. Set the roasting pan on the oven rack and pour in enough boiling water into it to come about halfway up the side of the springform.
Bake until the cake has risen slightly, edges are just beginning to set, a thin glazed crust (like a brownie) has formed on the surface and an instant read thermometer inserted halfway into the center of the cake registers 140F, about 22-25 minutes.
Remove the springform pan from the water bath and set on a wire rack. Cool to room temperature. Cover and refrigerate overnight to mellow.
Cake can be kept covered and refrigerated up to 4 days. About 30 minutes before serving, remove the springform pan sides, invert the cake on a sheet of waxed paper, peel off parchment pan liner, and turn cake right side up on a serving platter. Sift with powdered sugar for garnish