Chocolate ‘High-Ratio’ Sheet Cake

1. Preheat the oven to 350°F with a rack in the middle. Grease an 18-by-13-by-1-inch baking sheet.

2. Make the Cake: Place the cocoa powder in a medium heatproof bowl. Pour in 1½ cups boiling water and whisk to combine. Set aside to cool to room temperature.

3. In the bowl of a stand mixer fitted with the paddle attachment (or in a large bowl, using a hand mixer), cream the shortening, butter and sugar on medium-low speed until light and fluffy, about 4 minutes.

4. Add the eggs and egg yolks one at a time to the shortening mixture, mixing until each one is fully incorporated. Scrape the bowl well. Add the vanilla and mix to combine.

5. Sift together the cake flour, baking powder, baking soda and salt in a medium bowl. Add one third of the mixture to the shortening mixture and mix on low speed to incorporate. Add half the cooled cocoa mixture and mix to incorporate. Repeat, alternating the flour mixture and cocoa mixture, until both are fully incorporated and the batter is smooth.

6. Pour the batter into the prepared pan and use an offset spatula to spread it evenly. Bake the cake until a toothpick inserted in to the center comes out clean, 20 to 25 minutes. Let the cake cool completely in the pan.

7. Make the Ganache: Place the chocolate in a medium heatproof bowl. Bring the cream to a boil in a small saucepan over medium heat and immediately pour it over the chocolate. Let the mixture sit, undisturbed, for 15 seconds, then stir, beginning in the center of the bowl with small circular motions and widening the circles, until the ingredients are uniformly combined and the ganache is smooth. Let the ganache cool to room temperature (you can park it in the refrigerator to speed this up, but don’t let it firm up completely).

8. Transfer the cooled ganache to the bowl of a stand mixer fitted with the whisk attachment (or use a large bowl and a hand mixer). Whip the ganache on medium-high speed until lightened in color, about 3 minutes. Scrape the bowl well and whip again to make sure the ganache is fully aerated.

9. Scoop the ganache onto the cooled cake in the pan and spread it evenly to the edges.

Why it Works: High-ratio cakes traditionally use shortening, which is 100 percent fat, rather than butter, which is about 18 percent water—pure fat helps the ingredients in these ratios combine properly into a smooth batter. The texture of the cakes is light, tender, and moist, and it stays that way a bit longer than cakes made using other methods, all because of the higher ratios!

Pro Tip: This cake can also be baked in two 9-inch round cake pans—increase the baking time to 35 to 37 minutes.