Preparation Arrange a shelf in the lower third of the oven, place a baking stone on it, and preheat the oven to 350°F/177°C. Spray VERY GENEROUSLY a 13 x 9 x 2-inch (33 x 23 x 5-cm) rectangular pan or two 9 x 2-inch (23 x 5-cm) round cake pans with nonstick cooking spray. Line the bottom of the round pans with parchment and spray on top of the parchment. With the rectangular pan, line and extend up the long sides with a piece of Release foil or parchment sprayed lightly with nonstick cooking spray. In a heavy saucepan, stir together the sugar, salt, cocoa, and baking soda. In another saucepan, bring 1 cup (237 ml) water to a boil. Stirring constantly, pour boiling water a little at a time into the cocoa mixture. It will bubble up at first and then get dark and thicken. Stir the cocoa mixture briskly. Place on the heat and bring back to a boil. Turn off the heat and allow to stand in the hot saucepan for at least 10 minutes. Pour the hot cocoa mixture into a mixing bowl. Add the oil and vanilla and beat on low speed for about 10 seconds. On low speed, beat the flour into the batter and then, with a minimum of beating, beat in the egg yolks, whole eggs, and buttermilk. This is a thin batter. Pour the batter into the prepared pan or pans. Place in the oven on the stone and bake until the center feels springy to the touch, about 25 minutes for round layers or 35 minutes for the sheet cake. Allow to cool in the pan for about 10 minutes on a rack. Run a thin knife around the edge and jar the edge of the pan to loosen. Invert onto the serving platter. Cool completely before icing. From BakeWise by Shirley O. Corriher. Copyright © 2008 by Shirley O. Corriher. Excerpted by permission of Scribner. All rights reserved.Buy the full book from Amazon or Bookshop .