For the Cake:

1. Preheat the oven to 350°F with the rack positioned in the middle. Spray two 9 × 2-inch-high cake pans with vegetable oil and line with parchment. Spray the parchment.

2. Sift together the flours, baking soda, baking powder, and salt. Set aside.

3. Place the chocolate and cocoa powder in a bowl. Bring the coffee to just below a simmer and pour over the chocolate. Tap the bowl against your work surface so the chocolate settles into the liquid, and let sit 1 minute. Using a wire whisk, stir gently until the chocolate has melted and the mixture is smooth. Whisk in the buttermilk.

4. In the bowl of a standing mixer fitted with the paddle attachment, mix together the canola oil, sugars, and vanilla. Beat at medium speed for 2 minutes. Scrape down the sides of the bowl. Add the eggs one at a time and beat in at medium-high speed, scraping down the sides of the bowl after each addition. At low speed, in 3 additions, add the flour mixture and the chocolate mixture, alternating the two and scraping down the sides of the bowl after each addition. Mix until just combined. Do not over-mix or the cake will be tough.

5. Divide the batter between the 2 pans, filling the pans two-thirds of the way. Tap gently on your work surface once to disperse air bubbles and even out the batter. Place in the oven on the middle rack. Bake 25 minutes, then switch the pans from back to front and turn them 180°.

Bake for another 10 minutes. Test for doneness by lightly touching the top. It should spring back and the sides should be very slightly pulling away from the sides of the pan. If it does not seem done, leave for another 5 minutes and test again. Remove the cakes from the oven and cool on racks in the pans for 15 minutes, then invert onto a rack. Remove the pans and parchments, and cool completely.

6. When the cakes have cooled, use a long knife, an offset serrated knife, or a bread knife to cut away the domes so the cakes have flat, even surfaces. Place one cake on a round or on a plate and cover with the frosting, Place the other cake on top and cover the entire cake with frosting. Dimple the top and sides so it looks like the pictures on cake mix boxes.

For the White Mountain Frosting:

1. Combine 1 cup of sugar, the water, and the corn syrup in a heavy medium saucepan. Cover and place over medium-high heat for 4 minutes, or until the sugar has dissolved and the mixture is simmering. Insert a candy thermometer and boil until the mixture reaches 235°F. Remove from the heat.

2. Meanwhile, begin beating the egg whites in the bowl of a standing mixer fitted with the whisk attachment at medium speed. When they begin to foam, add the cream of tartar and 1 tablespoon of sugar. Continue to beat at medium speed while you slowly add the remaining 2 tablespoons sugar. When the egg whites form soft peaks, begin to slowly drizzle in the hot syrup while you beat at medium speed, drizzling it down the inside of the bowl and being careful not to drizzle it over the beaters. When all the syrup has been added, stop the mixer and scrape down the sides of the bowl. Add the vanilla and beat at high speed until the egg whites are stiff, glossy, and cool. The frosting will have lost quite a bit of volume from when it was just meringue; it will be dense and sticky, but stable and spreadable.