Marble Sheet Cake with Buttermilk Chocolate Frosting - A Recipe from Scratch

      Buttermilk appears twice in this recipe: first in the batter, where it helps make the crumb tender, and again in the frosting, where it balances the butter and sugar, enhancing the flavor of the chocolate as buttermilk typically does.

      Makes 1 (13x9-inch) cake

      1¼ cups (284 grams) unsalted butter, cubed and softened, divided

      2 cups (533 grams) granulated sugar

      ½ cup (112 grams) neutral oil

      4 large eggs (200 grams), at room temperature

      2½ teaspoons (10 grams) vanilla extract

      4 cups (500 grams) all-purpose flour

      1 tablespoon (15 grams) baking powder

      1 teaspoon kosher salt

      1¼ cups (300 grams) buttermilk, at room temperature

      2.5 ounces (70 grams) 60% cacao bittersweet chocolate, chopped

      3 tablespoons (15 grams) Dutch process cocoa powder

      Buttermilk Chocolate Frosting (recipe to follow)

      Preheat the oven to 350°F (180°C). Coat a 13x9-inch baking pan with baking spray that contains flour. Line the pan with parchment paper, allowing some to hang over the sides. In the bowl of a stand mixer fitted with the paddle attachment, cream together 1 cup (227 grams) of butter, granulated sugar, and oil at medium speed for 2 to 3 minutes, stopping to scrape down the sides of the bowl. Add the eggs one by one, beating well after each addition, and then mix in the vanilla.

      In a separate medium bowl, whisk together the flour, baking powder, and salt. With the mixer on low speed, gradually add the flour mixture to the butter mixture, alternating with the buttermilk, starting and finishing with the flour mixture, and mixing just until incorporated after each addition.

      In a large microwave-safe bowl, melt the chocolate in the microwave at high power in 30-second intervals, stirring between each session, until fully melted. Mix in the cocoa and remaining ¼ cup (57 grams) of butter until the butter has melted completely and everything is well mixed. Stir in one-third of the vanilla batter (approximately 2 2/3 cups or 620 grams) until combined.

      Spread half of the remaining vanilla batter (around 2 2/3 cups or 620 grams) in the bottom of the prepared pan. Drop spoonfuls of the chocolate batter and the remaining vanilla batter in a checkerboard pattern into the pan (5 scoops wide along the short side). Tap the pan on a kitchen towel-covered counter 2 to 3 times to help level the batter and fill the pan. Use a knife to create a zigzag swirl of the batters both lengthwise and widthwise. Tap the pan again to ensure the batter is level and fills any gaps.

      Bake until a wooden pick inserted into the center comes out with a few moist crumbs and an instant-read thermometer placed in the center reads between 200°F (93°C) and 205°F (96°C), approximately 50 to 55 minutes, covering with foil if needed to prevent excessive browning. Allow to cool in the pan for 10 minutes. Using the overhanging parchment paper as handles, remove the cake from the pan and let it cool completely on a wire rack. Once cooled, transfer the cake to a serving platter and spread the Buttermilk Chocolate Frosting on top. Using a small offset spatula, create texture or swirls as desired. Refrigerate, covered, for up to 5 days.

      Let us know how it turned out!

      Buttermilk Chocolate Frosting

      Makes 5 cups

      1½ cups (340 grams) unsalted butter, softened

      6 cups (720 grams) confectioners' sugar

      ¾ cup (64 grams) Dutch process cocoa powder

      1 teaspoon kosher salt

      ½ cup (120 grams) buttermilk, at room temperature

      In the bowl of a stand mixer fitted with the paddle attachment, beat the butter at medium speed until creamy. In a large bowl, combine the confectioners' sugar and sift the cocoa powder onto it. Add the salt and whisk to mix. With the mixer on low speed, gradually incorporate the sugar mixture into the butter, beating until well combined. Slowly add the buttermilk, mixing until the frosting reaches a spreadable consistency. Use immediately.

      Let us know how it turned out!