Chocolate & Yellow Swirl Cake W/ Chocolate Icing Recipe

Prepare and preheat

Preheat oven to 350°F (175°C). Grease and line two 8-inch (or one 9x13) round cake pans with parchment paper and lightly grease the sides.

Combine dry ingredients

In a medium bowl, whisk together 2.25 cups all-purpose flour, 1.5 cups granulated sugar, 2 tsp baking powder, and 0.5 tsp salt until well combined.

Cream butter and wet

In a large bowl or stand mixer fitted with the paddle attachment, beat 0.5 cup softened unsalted butter on medium speed until smooth. Add the dry ingredients in two additions alternately with the milk (0.75 cup) and buttermilk (0.5 cup), beginning and ending with the dry ingredients. Mix until just combined after each addition. Beat in 3 large eggs one at a time, scraping down the bowl between additions, then stir in 2 tsp vanilla extract. Do not overmix; the batter should be smooth and slightly thick.

Portion batter

Spoon about two-thirds of the yellow batter into a separate bowl (this will remain the yellow portion). Reserve the remaining one-third in the original bowl for forming the chocolate batter when combined with cocoa mixture (or use proportions described in the next section).

Make cocoa mixture

In a small bowl, sift or whisk together 0.75 cup unsweetened cocoa powder and 0.25 cup granulated sugar to remove lumps. Stir in 0.5 cup hot water until smooth to create a thick chocolate paste. Let cool slightly.

Combine with reserved batter

Add the chocolate mixture to the reserved one-third of the yellow batter. Stir until fully incorporated and the batter is uniformly chocolate. If the chocolate batter appears too thin, fold in 1-2 tablespoons of flour from the reserved dry ingredient measure (or add a tablespoon of sifted flour) to reach similar viscosity to the yellow batter.

Layer and swirl

Alternate spoonfuls of yellow and chocolate batter into the prepared pans: start with a large spoon of yellow batter in the center, then a spoon of chocolate batter on top; continue adding in concentric rings or alternating dollops until all batter is used. Use a small offset spatula or skewer to gently drag through the batter in an 'S' or figure-eight pattern to create a marbled swirl. Do not over-swirl.

Bake

Tap the pans gently on the counter to remove air pockets. Bake in the preheated 350°F (175°C) oven for 25–35 minutes for 8-inch rounds (or 30–40 minutes for a 9x13) until a toothpick inserted near the center comes out with a few moist crumbs but not wet batter. Rotate pans halfway through baking for even browning.

Cool

Remove cakes from oven and let cool in pans on a wire rack for 10–15 minutes. Run a knife around the edges, invert the cakes onto the rack, remove parchment, and cool completely (at least 1 hour) before icing.

Prepare butter and cocoa

In a medium bowl, cream 0.5 cup unsalted butter with 0.66 cup unsweetened cocoa powder until combined and fluffy. Use a mixer on low to medium speed to avoid cocoa flying out.

Add powdered sugar and milk

Gradually add 3 cups powdered sugar, about 1 cup at a time, mixing on low. Add 3 tablespoons whole milk and 1 tsp vanilla extract. Increase speed to medium and beat until smooth. If the frosting is too thick, add additional milk in 1 teaspoon increments until spreadable. If too thin, add up to 1/2 cup more powdered sugar.

Adjust seasoning

Taste and add 1/4 tsp salt if desired to balance sweetness. Beat another 20–30 seconds to incorporate.

Assemble and frost

Place one cooled cake layer on a serving plate or cake board. Spread a thin layer (crumb coat) of chocolate icing over the top; chill 10–15 minutes to set. Apply remaining icing evenly to top and sides with an offset spatula. If using a 9x13, simply spread all icing over the cooled cake. For an attractive finish, leave swirls or smooth with a spatula.

Garnish and set

Optionally sprinkle chocolate shavings or sprinkles on top. Chill for 20–30 minutes to set the icing slightly before slicing. Bring to room temperature 15 minutes before serving for best texture.

If using two 8-inch pans, split batter evenly between them for layered cake. If using one 9x13 pan, use all batter in that pan and bake until a toothpick comes out clean. Use parchment rounds for easier removal. Store leftover cake covered at room temperature for 2 days or refrigerated for up to 5 days.