Position rack in center of oven and preheat oven to 350 degrees. Butter, or coat with vegetable spray, two 9-inch round cake pans. Dust with flour, tapping out any excess flour. Set aside.

Sift together 1 cup sugar, the flour, cocoa, baking powder, baking soda, and salt. Set aside.

In the large bowl of an electric mixer, with paddle or beaters, beat the egg yolks at high speed. Turn speed to low and pour in the oil, water, and vanilla. Gradually add the sifted ingredients, and when almost incorporated, turn speed to medium, and beat until well combined. Remove bowl from machine.

In another clean large bowl, with whip or beaters, whip the 6 egg whites until soft peaks form. Start on medium speed and raise speed as peaks begin to form. Gradually pour in the remaining ½ cup sugar and whip until whites are shiny and firm but not stiff. With a rubber spatula, fold ¼ of the whites into the chocolate mixture, then scrape the chocolate mixture back into the whites, quickly folding until completely incorporated.

Scrape into the prepared pans, rap, and bake until edges of the cake pull away from the pan and a tester, gently inserted into the center of the cake, comes out clean, 30 minutes or more. Cool on a rack. To remove, run a sharp knife around the inside of the pan to loosen cake. Invert onto rack. Place 9-inch cardboard round on cake and invert cake onto round.

To serve, the cake can be served as is, confectioners' sugar sifted over the top, and a fanned strawberry arranged on the side. Slices of cake can be arranged on plates, with vanilla- or coffee-flavored Crème Anglaise spooned under or over the slices. The cake also can be cut into layers with a sharp, serrated knife, and Rich Chocolate Frosting spread between the layers.