Bittersweet Chocolate Cake Recipe

Preheat oven, prepare springform pan: Preheat oven to 325°F. Prepare a rack in the center of the oven. Place a baking sheet in a rack below it (to catch any drippings or spill-overs). Generously butter the sides and bottom of a 9-inch or 10-inch springform pan. Add a few tablespoons of sugar and gently shake so that all the sides and bottom of the pan are coated with sugar. Tap out excess sugar.

Beat egg yolks with sugar: Beat egg yolks with the granulated sugar until they are thick and pale yellow and form a ribbon when they fall from the beater, about 2 to 3 minutes on medium speed of an electric hand mixer.

Melt chocolate: Make a double boiler by heating an inch of water to a bare simmer in a saucepan, and place a metal bowl on top of it. Make sure that the bottom of the metal bowl is not touching the water below. Place chocolate and 4 Tbsp of water together in the top metal bowl of the double boiler. Slowly melt the chocolate over barely simmering water, whisking it until smooth. If the chocolate gets too thick, and looks like it will firm up, whisk in a tablespoon more of water. Whisk in a pinch of salt. Let cool until just warm to the touch.

Make batter base: Slowly fold the warm chocolate into the egg mixture, gently stirring while you add the chocolate. Stir in the softened butter. Stir in the grated orange peel. Stir in the sifted flour. Mix thoroughly but gently.

Incorporate beaten egg whites: Beat the egg whites until stiff. (See this wonderful explanation of whisking egg whites taken from La Bonne Cuisine de Madame Sant-Ange.) Stir one third of the beaten egg whites in to the chocolate egg mixture to thin it. Gently fold in the remaining beaten egg whites, a third at a time until the egg whites are completely incorporated. Be careful at this stage not to over-mix.

Bake: Pour the batter into your prepared springform pan. The batter will come close to the top of the pan. Set the pan on the middle rack of your oven and bake at 325°F for 1 hour and 20 minutes, or until a cake tester comes out clean, or a digital thermometer inserted into the center reaches 200°F (93°C). Do not worry if the top of your baked chocolate cake has cracks in it! As the cake cools the top will settle and the cracks will close.

Cool: Cool on a rack for 15 minutes, then remove the outer rim. Allow the cake to cool completely before removing the bottom of the pan. Refrigerate.

When ready to serve, sprinkle with powdered sugar.