Blackout Cake

Make the pudding: In a small bowl, whisk together ¼ cup milk and cornstarch until smooth. Set aside. In a medium saucepan, combine the remaining 1¾ cups milk, sugar, chocolate, cocoa powder, vanilla, and salt. Heat over medium-low heat, whisking, until chocolate is melted. Whisk in the cornstarch mixture until fully incorporated. Reduce the heat to low, and continue to stir briskly with a wooden spoon or a heatproof spatula. The mixture will come to a simmer and slowly begin to thicken. Continue to cook 1 to 2 minutes, or until the pudding coats the back of the spoon and slowly drips off. Remove from heat and transfer to a bowl. Cover with waxed paper directly on the surface. Chill well. You’ll have extra and that’s fine; keep it in your snack arsenal to dip into when no one else is around.

While pudding chills, make cake layers: Preheat oven to 350°F. Grease two 9-inch cake pans with butter and dust with flour. Line pans with parchment rounds and then grease the rounds.

In a large heavy saucepan over medium heat, bring the stout and butter to a simmer. Remove from heat and whisk in the cocoa powder until smooth. Let cool 5 minutes.

Whisk together the flour, sugar, baking soda and 1½ tsp salt in a large bowl. In a separate large bowl, whisk together the sour cream and eggs. Whisk the stout mixture into the egg mixture, and then, using a rubber spatula, stir in the flour mixture, until incorporated and the batter is smooth, scraping the bottom of the bowl to incorporate any dry bits. Divide the batter equally between pans and bake until a toothpick inserted in the center comes out clean, about 35 to 40 minutes. Transfer to a rack to cool completely.

Make the frosting and assemble the cake: Once you have cooled pudding, begin the frosting base. In the bowl of a stand mixer fitted with a paddle attachment, combine the butter, 3 cups confectioners’ sugar, cocoa powder, pudding (¾ cup), and ¼ tsp salt. Mix on low until just incorporated. Next beat on medium-high until the mixture is creamy and ingredients are incorporated, about 1 minute. Scrape down the sides of the bowl with a rubber spatula. Add more sugar, 1 cup at a time, and mix on low until the frosting is thick but spreadable. Beat for 1 minute after each addition. (You may not need to add all the remaining sugar.) Raise the speed to medium-high and beat for 3 to 4 minutes, or until very light and fluffy. If the buttercream appears too thick, add some cream, 1 Tbsp at a time. If it appears too thin, add more confectioners’ sugar, 1 heaping Tbsp at a time.

Once the cake layers have cooled, frost the cake with the dark chocolate pudding buttercream.