This marble cake recipe features vanilla cake swirled with chocolate for a gorgeous marble effect. The cake is covered in a silky smooth, whipped chocolate frosting.
Preheat the oven to 350°F Grease and lightly flour 2 9-inch round cake pans; set aside.
In a large bowl, beat the oil, butter, and sugar together until light and fluffy, about 5 minutes. Add the eggs, one at a time, mixing for about 20 seconds after each addition. Add the vanilla and mix for 20 seconds.
Combine the flour, baking powder, baking soda, and salt in a medium bowl. Stir with a whisk and add half to the butter mixture. Beat on medium-low speed until just combined. Add the buttermilk followed by the remaining flour. Beat on medium-low speed just until combined.
Remove ¾ cup of the cake batter and pour into a medium bowl. Add the cocoa powder and stir until well combined.
Divide the vanilla cake batter evenly between the prepared pans. Drop spoonfuls of the chocolate batter evenly over the batter in the pans. Use a knife to swirl the two batters together but take care not to combine them too much.
Bake for 20-30 minutes or until a toothpick inserted into the center comes out with few moist crumbs attached. Take care to not over-bake. Check the cake at 15 minutes to see how it is doing and judge the timing from there.
Cool for 10 minutes. Remove from pans and cool completely on a wire rack.
Make the frosting
Place chocolate in a heatproof bowl and set it over a pot of barely simmering water. Make sure the water isn't touching the bottom of the bowl. Stir the chocolate continuously until fully melted and smooth. Remove the bowl from the heat and stir until the chocolate is no longer warm to the touch.
In the bowl of a stand mixer fitted with the paddle attachment or with a handheld electric mixer, beat the butter on medium speed until smooth and creamy.
Add the melted and cooled chocolate. Beat on medium speed until well combined and fluffy.
Assemble the cake
Place one layer on a serving platter. Spread about ⅓ of the frosting over the top.
Gently place the second layer on top of the frosting. Spread remaining frosting over the top and sides of the cake.
Notes
Cake flour will give you the best texture. If you don't have cake flour, you can make it using my homemade cake flour recipe. Keep in mind this is not going to give you the exact results as real cake flour. Cake flour can be found on the baking aisle of your local supermarket.
Buttermilk is best for this recipe! If you don't have it, you can make it by adding 1 tablespoon of lemon juice to 1 cup of regular whole milk.
The cakes can also me made in three 8-inch round cake pans. The bake times may need to be adjusted slightly.
You can change the ratio of chocolate used for the frosting if desired. As long as the total amount of chocolate is equal to 24 ounces, you can use more or less of each to suit your palate.
Make ahead tips
Wrap baked and cooled cake layers tightly in plastic wrap and store them in the refrigerator. Assemble and frost the cake within 2 days.
Or layers can be triple wrapped in plastic wrap and frozen for up to 2 weeks. Leave wrapped and set on the counter to thaw slightly before use.
The frosting will keep for up to 3 days at room temperature, 3 weeks stored in the refrigerator, or 6 months in the freezer. Store it in an airtight container. You must let the buttercream come to room temperature by setting it out on the counter for a couple of hours, then beat it with an electric mixer if needed.
Once the cake has been assembled, cover it and store it at room temperature for up to 3 days or in the refrigerator for up to 5 days. Bring it to room temperature just before serving.
The frosted cake can be frozen for up to 2 months. Thaw it overnight in the refrigerator and let it come to room temperature just before serving.