Step 1
Preheat the oven to 350°F. Grease an 8x8x2-inch pan with nonstick cooking spray or softened butter. Line with parchment paper and grease again.
Step 2
To make the cake, add the Domino® Dark Brown Sugar, flour, cocoa powder, baking powder, baking soda, and salt to a large mixing bowl and whisk to combine.
Step 3
Add the egg, yolk, vanilla, oil, and buttermilk and whisk until smooth and combined.
Step 4
Add the boiling water and whisk until smooth.
Step 5
Pour the batter into the prepared pan and bake for 20 to 25 minutes, rotating at the halfway point. The cake is ready when a toothpick inserted in the middle comes out with a moist crumb or two. Let cool completely in the pan.
Step 6
Place a large heatproof bowl over a saucepan of simmering water over medium-high heat. Do not allow the bottom of the bowl to touch the water. Add the egg whites, Domino® Light Brown Sugar, cream of tartar, salt, and water.
Step 7
Using an electric hand mixer, beat the egg white mixture on high speed until stiff and glossy, about 7 minutes.
Step 8
Remove the bowl from the saucepan of hot water, add the vanilla, and continue beating for another 2 minutes.
Step 9
Generously frost the cake – either in the pan – or invert it on to a serving platter first. If you wish, you can decorate your cake with chocolate curls, chopped chocolate pieces, cocoa powder, or chocolate sprinkles!
The frosted cake is best served within a few hours as the frosting dries and weeps pretty quickly.
Be sure to vigorously whisk the cake ingredients together before transferring the batter to the prepared pan and do not over bake the cake. Pull it from the oven when there is still a moist crumb or two on your toothpick. Make sure you whisk your whites until stiff, glossy peaks form or your frosting will be droopy and loose. If you do not have a hand mixer, place the bowl of your stand mixer over the pot of simmering water and whisk by hand until the mixture is warm to the touch, then remove the bowl and place on your stand mixer and whisk until stiff and glossy peaks form.