This chocolate cake is a descendant from the famous chocolate cake made popular by advice columnist Abigail Van Buren (real name, Pauline Phillips) of the long-running “Dear Abby.” Where as hers was a layer cake covered in white meringue icing, this sheet cake version, based on the cake my friend Matt Piacentini’s late mother Louise made one summer for our vacation on the Oregon coast, uses an old-fashioned, cocoa-flavored American buttercream to frost just the top, resulting in the perfect ratio of frosting to cake. It’s the type of cake you’ll keep coming back to, cutting off squares here and there, until you’ve eaten half the cake yourself over a couple days. Spring for the good chocolate and cocoa powder to make it special, but the supermarket standards will also give you great results.
Chocolate Sheet Cake
1 hour, plus cooling. Serves 12 to 16.
For the cake:
- Nonstick baking spray
- 8 tablespoons unsalted butter, room temperature
- 4 ounces unsweetened chocolate
- 2 cups all-purpose flour
- 1 ¼ teaspoons baking soda
- 1 teaspoon fine sea salt
- 2 cups granulated sugar
- 1 cup sour cream (8 ounces)
- 1 ½ teaspoons pure vanilla extract
- 2 large eggs, beaten
For the frosting:
- 2 cups powdered sugar, sifted
- ¼ cup unsweetened cocoa powder, preferably Dutch-processed
- ¼ teaspoon fine sea salt
- 4 tablespoons unsalted butter, room temperature
- ¼ cup heavy cream, room temperature
- 1 teaspoon pure vanilla extract
- Heat the oven to 350 degrees. Grease a 9-by-13-by-2½-inch metal baking pan with baking spray.
- In a small saucepan, melt the butter and chocolate with 1 cup water over medium heat, stirring occasionally. Remove the pan from the heat and let cool to room temperature.
- In a large bowl, whisk together the flour, baking soda and salt. In a medium bowl, whisk together the sugar, sour cream, vanilla and eggs until smooth. Pour the chocolate mixture into the sour cream mixture and stir until smooth. Pour the liquid ingredients over the dry ingredients and stir until just combined. Pour the batter into the prepared pan and smooth the top. Bake until a toothpick inserted in the center of the cake comes out clean, 40 to 45 minutes.
- While the cake is in the oven, make the frosting: In a large bowl, whisk together the powdered sugar, cocoa powder and salt. Add the butter and beat with a hand mixer on low speed until evenly combined and clumpy. With the mixer still running, slowly drizzle in the cream and vanilla and beat, starting on low speed and gradually increasing to medium-high, until fluffy and spreadable, 1 to 2 minutes.
- Remove the cake from the oven, transfer to a wire rack, and let cool completely. Scrape the frosting onto the cake and use a small offset spatula or table knife to spread it evenly over the top before serving from the pan.
The cooled cake can be wrapped in plastic wrap and kept at room temperature for up to 2 days. The frosting can be refrigerated for up to 5 days. Return the frosting to room temperature before beating again and using.